Oh I dunno. . .
Ability to increase one's toons physical size, to that of a silver/black knight or larger
High dex/str or maybe the inclusion of different fighting forms that affect your moveset with certain weapons. (like once you hit the expert threshold for str for something like zweilander your character stops wielding it like he can barely lift it)
More magic, and magic that is different, and affects the battlefield and what not. (like maybe summong mobs?)
The ability for high sin players to be invaded while hollow
Covenants having more items and benefits that require players to have consistent interaction with them
A leaderboard for covenants
More useful items that require some amount of collection, like bombs/throwing knives that are feasible later in the game
The ability to replay bosses on a playthrough
Split screen co-op? (I know, it's controversial)
More status affects, that have to be used in more interesting ways (like having to be cursed to fight ghosts was awesome, the fact that transient curses existed ruined it)
Make the game generally darker, as in ToTG dark
Bring back carrying capacity on the character (and make lanterns slowly run out, so if the game had a ton of really dark areas, the player would have to stock up on multiple lanterns and do some inventory management and such)
MAKE NG+ AND NG++ AND NG+++ ETC SPAWN DIFFERENT/MORE ENEMIES, CHANGE BOSS FIGHTS TO MAKE THEM HARDER, AND GIVE A DIFFERENT EXPERIENCE, DON'T JUST MAKE EVERYTHING HAVE MORE HEALTH AND DO MORE DAMAGE. I WASN'T GETTING HIT DURING NG, JUST BECAUSE THEY DEAL MORE DAMAGE DOESn"T MEAN IT IS ANY HARDER, I'M STILL NOT GETTING HIT.
Make shields have way less stability, and very few block 100% physical
Make switching weapons and two handing weapons have more or less frames depending on the weight of the item you are switching to. Meaning you can't quickly switch between using a giant greatshield and then two handing a massive hammer.
Try to find ways to minimize the amount of invincibility frames players need, as in, give a combat system should players be knocked down.
Give a way to knock down players in relation to their stamina.
Raise the amount of players allowed in one world.
Allow planned two person invasions, perhaps as a covenant thing, that invade players with three+ people on their server.
Reduce farming by slowly making the souls from one area gained slowly diminish if players stay in that area and just consecutively use the bonfire and keep going back to the bonfire without challenging the boss. Also make this true to invaders killed. . . so yeah, ganking.
Make covenants that get specific perks and things from interacting with players of another covenant.
Get rid of equip load as the determining factor of mobility. Instead give armors mobility ratings that scale with specific stats. (I.e. light armor has S scaling with Dex and C with End, heavy armor has B with Str D with Dex and B with End, as well as armors having a base mobility rating)
Make elemental weapons less of a base damage deal, like perhaps hurting players who use them for the benefit of having unscaling high damage.
Make enchanted weapons have different benefits.
Buffing is the most OP thing in the game (not saying it can't be beaten, just it gives teh greatest advantage)
Recognize that players that do a ton of PvP are going to get more than 100 humanity, and need something to spend that humanity on/more use for humanity, as well as more use for souls of PvP heavy players. Perhaps good weapons that are very easy to break and cost a ton of souls to repair?? I dunno.
Make online work.
Add more depth to combat, with perhaps the ability to strike each others blades at a certain distance, more precise hitboxes that mirror models. Fixing deadangles, but making it so that more weapons have the shotel affect if they are actually hitting around the shield, and not having things like that shotel that automatically hit through shields even if they hit the shields. I dunno, tighten it up, make it good.
Give aiming reticles for magic users.
Make the crosshairs for the bows actually where the arrow goes.
Give a dex threshold for specific bows that allow more movement while firing ones bow.
Let arrows hit players in I frames.
Give more depth to the bow system.
Make low level magic (like soul arrow/fireball) for players with high dex/(int/fai) have very fast casts that can be done while jogging.
Make more unique weapons that have very special abilities, perhaps a straight sword that is also a catalyst/talisman.
Get rid of auto drops/let the player see the item they are trying to pick up before they accept it.
Make players that quit during invasions have the same affect as dieing.
Make high sin players able to be invaded even when the boss is dead.
Better enemy AI.
Better enemy AI.
Better, more intuitive weapon advancement system (basically right now, you either want chaos, lightning, or normal)
More cool online interaction, that work better, things along the lines of messages, and resonance rings.
Bosses that are more like the DLC bosses (They are by far the best, other than perhaps Orn and Smo)
Add more attacks to movesets by mapping more attacks onto the controller.
Make armors and enemies that are noticeable more resistant towards specific types of damage, I.e. slashing versus piercing
Add more longterm status affects with interesting affects, like egghead/curse.