One of my biggest concerns with Multiversus is just how far reaching its roster could be - you're gonna end up with a division between fans who want more DC heroes, more live action stars, more Cartoon Cartoons, more Hanna-Barbera, more Looney Tunes, so on - and then there'll be divisions of those divides, like people who want the live action characters to be kid-friendly and people who want the live action characters to be more adult; people who want to dive deep into the DC canon and people who want to include all the iconic heroes first; Looney Tunes purists who need everything to be classic and Space Jam fans hoping for modern favourites; 90s/2000s Cartoon Network fans wanting their childhood repped and 2010s Cartoon Network fans not wanting to settle for "nostalgia pandering", it could be a mess.
Another consequence of this "everything is fair game" approach is that a lot of really promising but more obscure characters could miss out because of it - you can have the Arrow, but Wild Dog? No chance. You can have Dexter, but don't hold your breath for Dial M for Monkey! - while it would mean less people playing, surely a specified roster would make those fewer people playing more statisfied?