The whole 10 classes, 10 playthroughs with different covenants thing holds up I think, but I believe there is more to it. I think you may have to role-play as different characters, I'm pretty sure Miyazaki even suggested that at one point. This is what I have so far, I don't know exactly who is who yet, & these are subject to change, as I believe as I'm playing through, who I will have to play as the other playthroughs will become obvious.
You also have to offer an ember on NG+ to one of the braziers in Firelink Shrine. You go through the game once, get all the equipment you need through the role-play, level up your covenant to at least +2, then on NG+ the actual role-playing begins. You can kill the character you are roleplaying in NG+, as you technically are that character, & it is almost like killing a fake you.
For all good covenants, you place the Lordvessal with Frampt, the evil with Kaathe, & neutral, you jump into Firelink on your own. As for linking the fire, I believe there are some exceptions. I believe Gravelords will link the fire, & that in Way of White you do not link it possibly, but since Cleric is last, I believe I will find the answer by that time.
You also have to choose the right gift I believe, either that, or you choose none for all except the last one, which you choose the pendant. I have not decided yet, so I will not list them, but some choices are obvious, like giving the Old Witch's Ring to the Pyromancer.
Also, I somewhat believe that each of these characters have a unique weapon that "belongs" to them. Oscar would get the Astoran Straight Sword, Pharis would get his bow etc. Some of these characters do not have one, so that could just be a dead end though. Either way, you would have to get all of their equipment to their highest level.
Oscar(or Solaire)/Warrior/Warrior of Sunlight/Astora/Large Ember?/No Serpent/Link the Fire
Could also be the Knight class, have not decided yet. I believe doing this playthrough will unlock all of his cut dialouge for the last playthrough, I'm not sure if the audio files are still in the game though, can someone help me on that?
Seigmeyer/Knight/Princess Guard/Catarina/Divine Ember/Frampt/Link the Fire
Dohmnall/Wanderer/Darkmoon Blade/Zena/Large Magic Ember?/Frampt/Link the Fire
Not sure about this one, I believe there is another character in the game that is from Zena, but we are not told directly they are from there. Any clues would be a tremendous help.
Lautrec/Theif/Darkwraith/Carim/Dark Ember/Kaathe/Walk Away
This one's a bit tricky, you cannot personally kill the Anastacia, so if anyone has any idea who you would play through that's from Carim besides him or Oswald let me know.
Shiva/Bandit/Gravelord/Far East/Large Fire?/Kaathe?/Walk Away?
Now I know most people are saying that he should be in the Forest Hunters, but I believe you are supposed to betray them. In his lost dialouge, he does eventually betray them, once he gets the Chaos Blade. You may be able to be Forest Hunter that first playthough, but I believe on NG+ that you are Gravelord.
Also, I believe he is possibly the one who killed Rhea. I read a theory on these boards awhile ago that made sense to me. They believed Petrus did not kill Rhea. They said he seemed to cowardly etc. & that Rhea did not have the pendant until she dies. They believe the murderer dropped it, & gave the Ivory Talisman to Petrus as proof that the deed was done.
Forest Hunters can get the Pendant through PVP, & in his unused dialouge, he says he wants to test the Chaos Blade on someone. I believe you have to talk to Petrus once he starts hating Rhea, kill her, drop the pendant near her corpse, then drop the Ivory Talisman near Petrus.
Pharis/Hunter/Forest Hunter/5 Finger Delta/Enchanted/No Serpent/Walk Away
I think in this playthrough, after doing Shiva's playthrough, his unused dialouge & black eye orb might become available. He betrays the covenant, & as Pharis you have to take him down
Quelana(possibly Laurentus, Salaman or Kirk)/Pyromancer/Chaos Servant/Great Swamp/Chaos Ember/No Serpent/Walk Away?
I mainly think it's Quelana because of the Old Witch's Ring, her getting this gift in the beginning would make sense lore-wise, & then when Quelaan calls her sister, it would be true(Though I think she uses Quelaag by name, so it could be Salaman) Since she has no special weapons, I believe the Ascended Flame counts as hers. Also believe she might have to link the flame, as the reason all of her kin got deformed is an attempt to recreate the first flame, so maybe fulfilling her mother's wish?
Logan?/Sorcerer/Dragon Path/Dragon Scholar/Crystal Ember/Kaathe?/Walk Away
Leeroy?(Possibly Petrus or Rhea)/Cleric/Way of White/Thorolund/Large Divine Ember/Frampt/Link the Fire?
Honestly, might be saying contradictory stuff here, but I also think Petrus might be innocent of even hiring Shiva to kill Rhea. Maybe he said some stuff that he did not mean, & Shiva took it as "Kill her", & he took her talisman in remorse almost, proof of his guilt & unintended crime. I believe that if all this stuff is true, I'll have figured it out by the last playthrough. Also, if stuff like Shiva's unused dialouge is used, that means I'm on the right track, & you possibly get the Elite Cleric Armor this playthrough, as a sort of confirmation that you have the right idea, & that you're supposed to play as Petrus. Could also let you advance in the covenant.
Now, the final playthrough is a little tricky. I think I might have to play as Solaire, but I'm not 100% on this. I believe the designers would not intend to take the true spotlight from the player, & that since this is the playthrough you would find out the secret of the pendant, you can name him anything, as YOU are the true chosen undead, especially since you are to figure out the secret of the pendant. All the other player characters online would just be fakes, as you were the one who found the true ending. Oscar would also be in the first & second playthrough, doing what he was intended to do, be your foil, if you're with Frampt, he tries to stop you & become the Dark Lord, & vice-versa.
Now first...the pandant. I believe that the false description was intended to be that. When Snuggly(could be Velka, which fits into this as you are trying to take down the gods for good & get the true ending) asks for warm & soft, I believe that you are supposed to give up your pendant, which with the false description has warm in it, & then the humanity which you just obtained from the first boss, as I can think of nothing else which could be "soft" besides humanity.
Second, the Sword of Artorias. A japanese player said a certain weapon fully upgraded is the only way to open a door. I believe that as an deprived, you are supposed to make this an uber-character, upgrade all stats, & that with that, Artorias' sword becomes the best weapon in the game. I think there might be a keyhole of some sort, & that with his blade, you are meant to use the stab attack to unlock said door. Even if this isn't the weapon you are supposed to use though, I believe I've thought this through enough where I could figure it out if it's something similar with a different weapon.
I believe you would have to have used all the covenants through 3 playthroughs. You would have to role-play each one though. First playthough, your main ending covenant is Darkmoon, as I believe that Gywndolin & Frampt are working together to continue the Age of Fire, & that that is not what Gywn even truly wants. This playthrough you may also use the Princess Guard & Chaos Servant Covenant. For all playthroughs you have a main covenant, & you can go one block away on the good/evil or chaotic/lawful line. In this playthrough, you would also make sure to save Solaire by getting chaos servant to +2, so he can help fight Gywn. I would dress as either a Silver Knight, or Black Knight during the final battle, not sure yet.
Next playthrough is mainly Darkwraith. Either in this playthough, or the last, I believe you have to do a no bonfire playthrough, if it's this one, you have to get all bonfires to max the first run, but if it's the last, you have one more run to get them all to max. During the final battle, you are a Darkwraith.
Fianlly, the last playthrough. You would be a sunbro, & that would also let you in the WoW & Gravelord covenants. Forest hunters also, though I think since they are true neutral, you may be able to start those during the other runs. You would have to offer the very large ember that playthrough. I'm leaning towards this playthrough being the no bonfire one, as I believe it would be the very last playthrough that you would kill the Everlasting Dragon, but time will tell. I don't know what else would happen obviously this playthrough, but I assume it'd blow my mortal mind if it was true haha.
Anyway, I know that was long, & there's honestly a lot more to it, I've been diving into the lore more & more recently, & there's a lot more evidence to this, but I believe this post has been long enough & I've made my point. Any helpful hints, or even constructive criticism showing some holes are appreciated(Just don't be too much of an ***hole lol)
Thank you, & good day.