I think the old republic thing could become interesting or really bad. I loved KOTOR and some lore from that time. The Revan plot was great and would've worked in movie/trilogy as well.
Is RJ really working on his trilogy? Wow, hope he kneels down every evening and thanks god that he still has a career after tlj.
KOTOR as a new trilogy would.be the dream. But has a trilogy been based on an already existing story? (I'm asking because I'm not knowledgeable enough of the whole expanded storyline)
Maybe just some bits and pieces of lore from the old republic would get in but not the actual KOTOR arc.
They can just do a one shot like Solo or Rogue One based on KOTOR and I bet a lot of fans would be happy.