One thing that I will avoid in this event is ending up with "perma-teams". The same people getting summoned. While others end up sitting around. That is counter-productive to the "open" nature of this event. Also, it would be nice to keep it as uncomplicated as possible. It's a trade-off, I know.
"I believe the sync works no matter how two people connect." Not really sure how this has relevance since my only concern is simply establishing a sync.
So, once the host makes a connection with all team members they do their x-number of runs and then the host resets the connection "potential". Rinse and repeat..summoning a set of different team members. I may be misunderstanding what you are saying Hugh...but I definitely don't won't a perma-team situation to develop leaving others to "sit on the benches" so, to speak. And simply having the host reset seems about as straight forward as it can get.
Your right about switching out hosts. But hosts are limited by whether they have their boss alive or not. Which is why Blightown would mean a brand new build or ng+. Both of which are doable if the "host" is willing.
Also, I am not limited to sl 100. As mentioned before, I will vary the soul level for technical reasons and a little variety. I'll prolly stay around sl 55/60, sl 80, and sl 100 for various events. At this point in the game even someone with a sl 55 has killed Pinwheel for the Rite of Kindling. It's one of the first things I do at sl 1-10 (usually) since I do a lot of low level run throughs
I believe you went to ng+ so that you could host the Catacombs and that was much appreciated. But, I couldn't expect that of others as a matter of course for each event. And unfortunately not everyone has the luxury (or wants it) to make new builds for each event. That would be asking a lot. I feel.
I'm not sure what you mean by "I assumed at sl 100 NG+ was standard..." unless you are referring to simply having bosses alive to host? If that be the case...Hosts had already been secured. Two actually: Bees and myself. Luckily, as it turned out you were able to host as was Luvz and Rant. So, we had four hosts!!
Your two hosts sync'ing idea is a thought but I wonder if then they would also end up sync'ing with the same team members? Which, again would lead to "perma-team' situation, I fear. I don't know about that one.