I started playing through Genealogy of the Holy War last year (after finally catching up with most of the Fire Emblem games released in North America; the only ones I haven't finished now are Shadow Dragon and two routes of Three Houses, the latter of which I'm planning to start soon). The game really is super intriguing from a story and character standpoint, but yeah, it needs a full on remake from a gameplay perspective. There are a lot of interesting ideas with the large maps and mission structure, and how the romance and timeskip is implemented, but the game is hard to play in a lot of respects. I would love to see it remade, and with Koei Tecmo apparently taking a larger role on Three Houses than we initially thought, it makes a certain amount of sense that a remake is something other people at Intelligent Systems would have been working in the meanwhile.
I wouldn't hold my breathe for Thracia 776 as DLC though. I know people have speculated on that, or even both games being remade into a single package, but I don't think either scenario is feasible when you consider Intelligent Systems turned Gaiden into such a fleshed out, robust game with Shadows of Valentia due to the care and attention they approached the remake with. I think Thracia 776 would have to be its own remake.
Overall, it was interesting to read through this feature as always!