Well, yeah, the original Ultimas are on Gog, but they make vanilla Dwarf Fortress look like Crysis.
I'd like modern, real remakes (with upgraded visuals and audio, and resolution scaling!) of the games that I loved from 20-30 years ago, the Ultimas for sure, Veil of Darkness, some of the lesser known classics that would probably still play reasonably well, mechanics wise. Nostalgia would get me to part with some cash, at the very least. Trying to play Betrayal at Krondor now assaults my eyeballs, for example, and I'd pay for a well done remake. Early 90s example: Crusader: No Remorse is on Gog, and I own it, but it runs like absolute crap, and is basically unplayable. More than a few old games on GoG are in that category: yes, it technically runs, but may or may not be playable/viewable for various reasons.
Still, it's probably a hard sell to most studios to do remakes of truly
old games; there are license issues, nobody has the source code or scripts usually, original art assets are gone, etc. etc. Look at all the trouble Beamdog went through doing the BG1 and BG2 Enhanced Editions, and that was with Bioware's help.