I found about this game the other day:

https://www.thedarkmod.com/main/

Is this the kind of game that GOG could host?

What about a game like Black Mesa?

If there's a thread for this kind of topic, can you provide a link and I'll bookmark it for future suggestions.

You can wishlist it here :)

Why would GOG want this, it is a free fan mod based on Doom 3. GOG is a business store, they are here to make money, not host files for no reason. If you want that mod, or any other mod, use moddb or nexus, or the mod web page.

Is it weird that there is no dedicated thread for this in the app? Why is that? I'm not into having to login into multiple platforms for stuff like this. Thanks for the link though but I'm not sure how much good wishlising games there will do. GOG gives away games for free regularly. There is a convenience factor of having one place for all your games and any content can drive customers to a site. No one ever complained that a store has too much stuff in it, I don't think.

GOG would still have to agree with the authors of the mod, and possibly even the engine, that GOG can host the file.

And that point the authors might ask GOG "since you want it so bad, how much are you willing to pay us for it?". After all, if GOG feels it is a good business decision to host such a free game (to get more people to join the store and possibly buy some other games here), the authors might feel they'd want some of that business profit as well, even if it is a free game.

Also, if GOG started hosting the game, GOG would have to offer support for it as well, with people complaining it doesn't work on their PC, complaining that the GOG version is not fully up to date or doesn't have achievements in Galaxy nor cloud save support, demanding GOG to remove the free game from their accounts and put it back and remove and put it back and remove and put it back, for shits and giggles.

I don't see much point in that, even from GOG's perspective, even if GOG didn't have to pay or negotiate with the authors at all. After all, that game can be freely downloaded from that site you linked to, so why not just get it there instead?

Afraid not. This has been discussed over and over. GOG would need to put in resources to acquire the rights, provide storage, download, product packaging, and support, and for all this effort they would get no return. In any business terms that is a a bad deal. If you want a convineint all in one place look at software like playnite and launch box.
As for driving gamers to the site, that would be a tiny number, anyone who has ever used a mod or patch knows that moddb and nexus mods is the place to go to. The dark mod is exactly that, a standalone mod based on Doom 3 engine.

Interestingly, apparently GOG just released OpenTTD for free.

So yeah, apparently they sometimes do that. You never know. However, I am much more interested in today's Sleeping Dogs and Thi4f releases, than OpenTTD. And somehow I feel I'd get OpenTTD from elsewhere anyway, as I am unsure if GOG will keep such an open source game up to date anyway.

Yes, and it will likely get proprietary locked into galaxy here for our benefit (like achievements, cloud saves etc.). Not interested in it, but if I was I would get it from the original site. They do occasionally add things for compatability - such as Vampire The Masquerade, but it causes more issues than it solves, the one here is out of date for instance.

The answer is in your title - mod.

GOG sell games not mods, though I guess some DLCs qualify as a mod, but generally they aren't standalone.

And even though you could say it is a mod for Doom 3, so perhaps a kind of DLC, Doom games have many mods, so where would you draw the line?

Personally, I see the Dark Mod as a specialist thing, not really something you get at the GOG General Store.

I also don't believe in having all your games in one basket, so I'd vote against it ... but each to their own.

There are apps, as has been suggested, that allow you the illusion of having all your games in one place.

P.S. That said, I kind of do have all my games in one place ... my Archives ... except for those that aren't DRM-Free, which in reality aren't my games anyway ... just borrowed.