[quote]What caused the lack of interest in the prior attempts?[/quote]
The lack of overall focus. You have it down in the third question so I'm fetching a guess you already knew. The main trouble I see is often people go off and do their own thing. Write some fantastic stories, but end up excluding several interested parties. 

[quote]Did a lack of a true multiverse setting, which is unrestrained by the contradictory limiting factors of crapton and importantnobody's kill interest?[/quote]
I wasn't around for this period. I could only speak for Rilla's attempt cause I was accepting characters at that time. And took over briefly before giving up as well. In which case it wasn't truly a multiverse setting either, but then again people seemed to flinch when characters started getting powerful enough to manipulate the energies of suns and entire worlds. The community here seems more comfortable with T5 and T6 on the AnimeLeague scale so I don't think a true multiverse setting would be adapted particularly well here. 

[quote]Did the lack of overall focus kill interest?[/quote]
Yes. That and previous attempts were too GM oriented. When the GMs get burned out or lose interests things grind to a halt until someone takes over. 

[quote]If you have an idea or want to comment please feel free. I am trying to gauge interest.[/quote]
New attempts should be made more robust by including some community feature that allows everyone to participate in all ideas in the multiverse without being overly restrictive in a wall of text. Rules are needed, but keep them simple so an elementary kid can understand them. As for enforcing these rules, talking it out with the person usually works. Reporting harassment if they persist on breaking the rules works also.