I saw this video the other day about a game I never heard of called Rusty (A Castlevania-style game).
The creator says in the comments he owns the rights to the game and is considering publishing if there is interest.

Here is the video link: https://youtu.be/LkDgnNr4kIw

I think this is a perfect game for GOG.

I've heard of Rusty, also saw the thumbnail on the YT recently so I guess it's the same video.

For me personally, any game from pc-88 & 98, x68k, fm-towns, msx 1 & 2, pc-engine, etc that gets ported and gets decent localisation for the west is a big plus. I absolutely love the artwork and sound of many games on these systems, pc-88 and 98 games are known to use a lot of dithering as a signature style of sorts (aside from being a tech.limitation workaround), which I really like. Only thing that ever held me back was often the lack of official or fan-made translations, which made these systems rather obscure, but nevertheless still very interesting to me.

Don't know whether it's too niche or not for gog though.