There is a not so tiny bit difference though.
For D:OS, people already see alpha footage, they know what is done already, what they might wanna tweak, what could be added, discuss stretch goal implementation, all efforts are done to improve the main game and are in line with Larian's primary goal.
For mod group, yes, like I said you can still post like "Zombie mod thread"( these days every game has a freaking zombie mode). When that's done, if you know how to build assets, that would be cool. Or to write back story and dialogs, like every game pre-production did.
BUT, for Larian's interest, it would be best to keep players' attention to main game, right? It doesn't hurt to create a sub-group, I'm not against it. But to demand stuff you want "right naw!" is a bit too aggressive, consider they just went through a 30 days social media marathon. Be a bit patient okay?