As a big super hero fan, I love a good Crisis Crossover. I'd be so down for it if other people would like to do it.
I would like to say something about crossover types and the logistics, though. As said, it's certainly a complex task to execute, so I feel the best way to give it unity is for everyone to kind of agree on a plot, to plot it all together, and then one person goes and writes it, submitting it to the others, who should be critical of course, but reasonable. It's no use thinking X character should have more face time if it's not the best for the story, even if it's yours. A variant would be that each writer writes different chapters of it.
@aqua03, you mentioned everyone writing its own character, each section. That's been done before, it's cool. Do you know 52? Four writers teamed up for this weakly series for DC in which each one had some ''nucleus'' of characters, that would appear less or more depending on the issue at hand. The only question is the type of crossover this would be.
There's a difference between crossovers like Crisis on Infinite Earths or Secret Wars and stuff like Punisher meets Archie (which is freaking awesome) or JLA vs Avengers.
The first type is driven by the universe's stories. Crisis puts dozens and dozens of character sharing the same story to deliver character moments that will change its characters, plot developments that are part of an ongoing story. The second is more about throwing different concepts at odds, celebrating them, and they usually have much less (to no) lasting impact on the characters lives.
The ''52 model'' would really work for the second type, the ''different universes'' crossover, which would be the logical (and easier) thing for Tapas. 52 didn't really had the storylines converging, each nucleus had its climax, so it was okay for each writer to write its portion of the book.
For something more ambitious, like Crisis or Secret Wars, for something that would be massive and ''in canon'', I believe a focused scripting method or at least a variation of focus and collaboration between writers would work best.
And as I said before and as it shows by my looong post, I'd be super down for it. I would love to try it!
(Also, I dig me some Riverdale. Some sexy CW soap opera)