New demo:

Sandwalkers: The Fourteenth Caravan

EDIT: The news post showed up a couple of minutes later.

Do note that if you install both, they install in the same directory, one on top of the other (like a DLC). I had to move one elsewhere to allow me to compare them.

Well, that's not true at all. Bitmaps and wave files can be compressed extremely well.
If you try to compress already compressed media, that's another story.
Ogg and png can be compressed a bit, but it's not worth the processing power for aac or jpeg.

ps: A good packager can also find similarities over different files and not compress each one on it's own.
So if the game was badly optimized and used the same resource in several files, that can make quite a difference.

New release:

Stay Out of the House

Just one of a couple titles with this particular retro-aesthetic to be released in a few minutes?
For instance, I remember Alisa having been confirmed a while back to get a release on GoG.

New edition:

Sins of a Solar Empire - Ultimate Edition

Note: There were way more releases today than visible news from the GOG.com front page. They all seem to have been attached to news posts, but they already scrolled off the "news" area so you have to dig into the forums.

Hunie Pop 2 Unrated free DLC is out now:
https://www.gog.com/en/game/huniepop_2_double_date_unrated

At the time of writing it's also not region-locked so grab it while you can if you're in Australia, China, Germany, Japan, and the other countries that usually block unrated patches.

New DLCs and new bundle (not mentioned in this post):

SAMUDRA - Digital Artbook
SAMUDRA Original Soundtrack
Lifeslide Soundtrack
Lifeslide + Original Soundtrack Bundle

New DLC:

Steelrising - Cagliostro's Secrets

Not sure if it fits here, but I thought what the harm in posting.

Toaplan shmups coming to GOG!
https://www.gog.com/en/game/twin_cobra
https://www.gog.com/en/game/truxton
https://www.gog.com/en/game/out_zone
https://www.gog.com/en/game/zero_wing

It doesn't, as the thread is about unanounced new games, those mentioned haven't been released yet - what's more, today there was a news post about them coming soon.

Aside from that, I just wanted to point out to the readers of this thread, that in my opinion something has recently changed in GOG's habits around 2-3 weeks ago and we recently got much more news about DLCs, and release news have more info about new editions as well. Way to go, GOG! :-)

My apologies.

A definite chance is that they ended that "experiment" with one-liners and actually seem to have someone write the articles again.

I see a few new games in catalog as coming soon, and news posts for them showing up, but not linked to from the front page. So probably coming soon.

https://www.gog.com/game/combustion
https://www.gog.com/game/phantom_fury
https://www.gog.com/en/game/fabled_lands
https://www.gog.com/game/fabled_lands_demo

...and they were posted in the minute it took me to write this and get the links.

I think this is worth linking to: Apparently Kynseed left InDev a couple days ago and is now a real title. No announcement.