What's been teased for GOG's 16th anniversary in September might be something different they have been working on alongside the RE PC port re-releases.
Both RE 2 & 3 (or just 2, and 3 just in time for the end of Shocktober) might be released then too, but they're not going to be the main attraction. Which, again, is likely something completely unexpected, like Diablo 2 + LoD, Nocturne, Dark Earth, No One Lives Forever 1+2, Oni, MechCommander 1+2, the Dune games, Discworld, etc.
Something that, over the years has amassed a shitload of votes on the community wishlist:
https://www.gog.com/wishlist/games#order=votes_total