Marioface5: I know this probably isn't it, but maybe the return of the Fallout series? It's been about two years since the removal, and it would be quite the surprise as mentioned earlier. Given Bethesda's (currently ridiculous) claim a while ago that "we’re anti-DRM as far as we can be" it would make sense if they had been making plans to bring their stuff to GOG. Like I said, this probably isn't it, but I can dream.
What you wrote may not seem as improbable as some may think.
Fallout series disappeared from GOG in late 2013.
And earlier Judas had written (referring to the hint):
I'm working on one but not sure how to go about it since the surprise coming soon-ish is quite the surprise and I want no spoilers at all It could even be Fallout 1-3 (I'd hope)
When Judas dropped the hint for
Mount&Blade the entire M&B game series was released in a row.