The makers of Hands of Necromancy (a Hexen-ish game on the GZDoom engine) would like to bring it to GOG: https://forums.duke4.net/topic/11985-hands-of-necromancy-a-fps-heretichexen-like-mixed-with-wonder-boy-3-dragons-trap-concept/page__view__findpost__p__370432

The Enhanced Edition of Oddworld: Soulstorm is getting a release on the consoles as well as the PC on the 21st of June.
So far, it's only been officially confirmed for the other distribution platform but might join the other titles of the franchise on GoG too, maybe even day 1.

"Gothic but in top-down 2D" dubbed Drova: Forsaken Kin has struck a publishing as well as financing deal with Deck13.
Just2D Interactive GmbH, the developer behind Drova: Forsaken Kin already have expressed their willingness to release on GoG, but with Deck13 taking over publishing duties it's now even more likely for Drova: Forsaken Kin to show up here once it's finished.

Another renamed game forum: "Seed of the Dead: Sweet Home" has been renamed to "Seed of the Dead".
Looks like we're getting the first game in the series as well.

Short Sleeve Studio's debut 2D hand-drawn point&click adventure Voodoo Detective "may release (on GoG) after launch".

This is proof that more people should get off their asses and contact developers directly if they want their games on GOG. Maybe it won't work much with the big ones, but indie devs can be convinced.

Not sure what this tweet from SEGA means, but something is coming to GOG....?
https://twitter.com/SEGA/status/1533478779619786752

Heilige Scheisse, it's happening.

Aliens: Colonial Marines, obviously.

Please no XD

It would be a very lousy joke to officially get SEGA on board - only to receive one of the biggest "hype turds" in the History of Video-gaming (beggars can't be choosers, though).

Although it could also be the Sci-fi Endless series

...who am I kidding?... It's probably Aliens:CM X(

It could also likely be Alien: Isolation (base game was given away for free at Epic), and maybe the 'classic' SEGA Warhammer games in keeping with GOG's hint about more upcoming classic Warhammer games incoming. Anyhow, this is definitely better than nothing, but I fear it'll be similar to Square Enix and we never see any of their Japanese games here. I really hope I'm wrong.

SEGA finally noticed us.

It would be very cool if the "new game source" they signed on turns out to be SEGA... and that would explain why they'd see an uptick in revenue.

While I was obviously joking but at the same time wouldn't rule out Colonial Marines just yet, it's probably:

Aliens vs. Predator (2010)
or
Alien: Isolation

Also:

Maybe Dawn of War ? It could be in line with the add during the "Skulls" event, about classic Warhammer games coming to GoG.