Yea this is difficult, mostly because of how subjective it is. Even looking at Ultima VII, that was a good pick considering how relatively few people on ERA seem to have played it, but at the same time CRPG veterans would say "nah U7 isn't even remotely 'hidden gem,' it's a classic."
This thread sprang up out of the discord lifeboat for the Essential RPG list and ultimately I think that list is the best litmus test for how well-known something is in this community, and how much of a "hidden gem" it is. If it made it on the list at some point then I consider it sufficiently well-known and played. So I would consider Planescape to be sufficiently well-known despite the fact that there are many members here who have never played it. On the other hand I would consider Ultima 7 more hidden because it never appeared on any version of the essential list iirc. And this is despite the fact that, on paper both of them are time-honored CRPG classics. Yet there is a tangible difference to me between how much Planescape is played in this community vs. Ultima 7. This ties into my belief that in this community, the absolute least-played major RPGs are CRPGs that pre-date the IE games of the late '90s.
That being said, I think it's ok for Planescape to be a nomination, ultimately the vote is the final determinant for what people consider to be an appropriate RPG to play through.
Also, re: Devil Survivor, I wouldn't worry too much about accessibility. I feel like requiring a 2DS/3DS is fine, sure it will restrict who can participate to an extent, but that will always be the case unless we just do a game available on PC over and over again, and even then some people won't have access to a PC that can run games decently.
