I believe I wrote the original version of that list, but it only included planes and planeswalkers who didn't have their own threads in the Archive, and of course it's now horribly out of date.
But honestly, even for our well-established characters and planes, it would be very useful, particularly as a navigation tool. And those who are not familiar with our Archives or even our project will find that a lot easier to use than just the Archives for finding particular stories.
Yes, this is one of the reasons I brought it up. Despite being one of the early M:EMbers, I'm quite unfamiliar with the current state of the project. The archive map is a great thing and an index could also be a great thing. I personally feel that I can't responsibly write more for the M:EM if I don't know what's already written, but don't know what order to read things in, or what places and characters already exist...
Ideally, an index would include 6 types of entries:
1. planeswalkers
2. legends (any important characters who aren't planeswalkers)
3. organizations (like the Cabal and the Coven)
4. planes (and the Dark Spot, and groups of planes like the Wheel and Helkavin)
5. locations that don't yet have a defined plane
6. major events (like the Ending War, and the collapse of Taramir)
I suppose that considering the Cabal records, that "characters who may or may not be planeswalkers, or may or may not have ever existed" could be rolled into Legends or given a 7th category.
Major Artifacts could be a category if you guys think that's worthwhile, too.