Actually, Xenosaga was meant to be a prequel and parts 1, 2, and 3 of a 6-part series that Xenogears was meant to be I believe the 5th game of. I think they abandoned that plan after the 2nd installment flopped, but it was originally meant to be pretty strongly connected.
Actually, Xenosaga was meant to be a 6-part game, but after the disaster of Part 2's reception, parts 3, 4, 5, and 6's storylines were condensed into one game and released as part 3 (at least they didn't just drop the project, like what happened to Shenmue). Xenogears was never meant to be part 5 or anything like that.
It was only really a prequel in that it happened thousands of years before Xenogears in the same universe, not really a direct
Although it is kinda ironic how the condensing of those parts into part 3 mirrors the budget problems that caused the middle third of Xenogears to basically become a visual novel.
For what I'd actually want to see in a remake? Easy, I'd want that middle third of the game taken out of VN territory, and properly expanded to RPG standards, so it matches the rest of the game.