Phantasy Star, the single-player series. We received one for GBA but it didn't include 4, which is the best one by far imo.
Just a rerelease of Arc the Lad Collection would be cool, but there were also a couple of releases after the PS1 collection.
Xenosaga would be my most wanted, I'd even be happy with straight ports that don't have any form of enhancements as I just want to replay the series.
Onimusha would be awesome, they have just abandoned the series at this point so a collection for contemporary platforms would be a good way to bring new fans in for a new main-series title.
Final Fantasy Tactics, including WotL, Advance, and A2. It would be awesome on Switch or 3DS.
Front Mission. We need more mecha SRPG goodness and I don't see us getting a new one following Evolved, which was a trainwreck despite its IP.
Others I would like to see are Wild Arms, Breath of Fire, Suikoden, Dot Hack (props to the other person who mentioned it!), Valkyrie Profile, Golden Sun, Camelot Mario Sports, Shadow Hearts, etc. Just a lot of JRPGs and SRPGs that I've missed because they were abandoned.
Perhaps instead of a Valkyrie Profile collection, a "Tri-Ace Best" collection would work that included Radiata Stories. I really like Radiata Stories.
I'd also like to see Zone of the Enders come to PS4/Xbone/PC but that's a pipe dream (not that the rest of these aren't, of course, but if I'm gonna dream I'm gonna dream big).
Edit: Grandia is another I didn't think of immediately, but there are enough titles to justify a collection imo. Also, a Mario RPG collection with the Mario and Luigi games, Paper Mario, Super Mario RPG, etc would be sick. Let's not forget about Earthbound/Mother, but we all know that isn't happening...
