Maybe we can make GOG staff reconsider. It has happened before.

List of cRPG's rejected by GOG (most of them due to being "too niche" for GOG):

The Quest - Islands of Ice and Fire expansion
Steamspy:
Release date: Feb 19, 2016
Price: $9.99
Userscore: 88%
Owners: 6,153 ± 2,004
Votes on GOG: 186

The Quest's generic name is really hurting it's visibility.

Antharion
Steamspy:
Release date: Jul 15, 2015
Price: $14.99
Userscore: 70%
Owners: 6,145 ± 1,692
Votes on GOG: 91

Ruzar - The Life Stone
Steamspy:
Release date: Dec 2, 2015 (previously in Early Access)
Price: $12.99
Owners: 2,680 ± 756
Votes on GOG: 75

The Fall of the Dungeon Guardians
Steamspy:
Release date: Nov 6, 2015
Price: $19.99
Userscore: 83%
Owners: 10,132 ± 2,160
Votes on GOG: 391

UnReal World
Steamspy:
Price: $10.99
Userscore: 97%
Owners: 7,246 ± 1,710
Votes on GOG: 254

KeeperRL
Steamspy:
Release date: Mar 31, 2015
Price: $14.99
Userscore: 91%
Owners: 12,819 ± 2,497
Votes on GOG: 49

Loren The Amazon Princess
Steamspy:
Release date: Jan 15, 2014
Price: $19.99
Userscore: 80%
Owners: 77,634 ± 6,292
Votes on GOG: 169

Planet Stronghold
Steamspy:
Release date: May 5, 2014
Price: $18.99
Userscore: 56%
Owners: 38,350 ± 4,463
Votes on GOG: 57

Excelsior Phase One: Lysandia
Votes on GOG: 23

Excelsior Phase Two: Errondor
Votes on GOG: 20

Dr. Dungeon's MADMAN!
Greenlit on Steam
Votes on GOG: 107

Nethergate
Votes on GOG: 185

Nethergate: Resurrection
Steamspy:
Release date: Oct 5, 2012
Price: $4.99
Owners: 58,005 ± 5,972
Votes on GOG: 320

Dungeon Lords (dev seem to have gone defunct)
Steamspy:
Release date: Dec 21, 2015
Price: $14.99
Userscore: 78%
Owners: 2,900 ± 1,335
Votes on GOG: 236

Starward Rogue
Steamspy:
Release date: Jan 22, 2016
Price: $11.99
Userscore: 98%
Owners: 6,284 ± 1,966
Votes on GOG: 181

Dungeons Of Dredmor
Steamspy:
Release date: Jul 13, 2011
Price: $4.99
Userscore: 95%
Owners: 566,359 ± 18,648
Votes on GOG: 646

Anyone remember any other cRPG's GOG has rejected?

Also probably rejected but not yet confirmed (It's been 5 months since last word from dev):

ADOM (Ancient Domains Of Mystery)
Steamspy:
Release date: Nov 16, 2015
Price: $14.99
Userscore: 90%
Owners: 16,022 ± 2,276
Votes on GOG: 82


Edit: Removed Dex as it was just approved by GOG on developers third try and is coming to GOG so keep on voting! Rejection is not the end!

Edit 2: Added Excelsior Phase One: Lysandia, Excelsior Phase Two: Errondor, Dr. Dungeon's MADMAN!, Nethergate, Nethergate: Resurrection, Dungeon Lords, Starward Rogue and Dungeons Of Dredmor

Well, this is the last communication on the matter from 5 months ago: Last steam update on the game is from 30th of January. That's when they added steam trading cards. So while there's more content coming in, it's not like game is constantly being updated on Steam. I asked them for an update on the matter but in the meantime, it does not hurt to raise awareness and get more votes in.

Hmm, Dex was rejected, why? (voted)

I love the graphical/art style of The Quest, it's just amazing

Per Farkeman on the game's wishlist comments:

Well, it's sad, I can imagine that 1st versions were buggy and its could lead to rejection but I thought that with EE everything would be fine. Shame, it seems to be nice game. Oh well, steam someday...

Voted for ADOM, Dex, KeeperRL, Loren, The Quest and Unreal World.

Ack! Don't do something crazy, man! At the very least, you can get it DRM-Free on the Humble Store. Alternatively, the developer is Kickstarting their next game, <span class="bold">Ghost Theory</span>, and you can add a copy of Dex to your rewards for 75% less than the retail price.

Tbh I saw box version in some polish shop for ~7 euro... I just think that it's steam version. :P

Doing the math, if you back their KS at the lowest tier and add Dex to your pledge, you can get it DRM-Free for ~7 Euro.

Where does it say that the Dex provided in KS is DRM-free? As far as I can see, it only says you get digital copy+OST. All the campaing page says is you can choose between Steam key+DRM-free version and console version of the Ghost Theory. Not that I would back an adventure game in any case, much less a horror game.

I reached out to the developers to get official clarification. Unfortunately, my assumption was incorrect. The add-on for the Ghost Theory campaign is Steam-only. Sorry for getting anyone's hopes up. :(

Voted. But otherwise I'll just be using this list of stuff I know to buy... elsewhere.

I have voted for a few of these. I think one of the things keeping them from being here is the price, some are just very expensive for what they look like.