I've always adored the story of the .hack//Universe, even if it is spread out (as with novels, manga, anime + games) even more than KH and still own the original 4 games on PS2, but they certainly do not age well.
The original 4 could arguably use a full remake, they are the very groundwork of the whole thing alongside the anime //sign after all, but I'm not sure if there is enough of a market for it.
I've never followed the G.U. series that much outside the manga (which was the only part of the second generation available in Germany, the games and anime were, unlike the first generation, never released here), so that Terminal Disk would certainly be a boon to catch up with the lore.