Bandai ran the Gundam brand into the ground here. Shogun Warriors has huge nostalgia value and the license is much cheaper.
Marvel's Shogun Warriors comics didn't use AI, I think they had human pilot characters. They just weren't the characters from the original show (and kinda boring, tbh). Either Raideen or Combattler was piloted by a black guy with an enormous afro, for instance.
Gaiking's original colors would look garbagey in live-action (and they're pretty garish in the original). I like the more detailed look combined with Gaiking's truly ridiculous giant horns and crazy skull-face. If they find a way to keep Face Open in, it will be glorious.
Honestly original Gaiking doesn't have very memorable characters except Pete, that's the only guy I'd like to see a version of in the cast. Don't even bother to call him Pete, just make him a carrier commander who is a complete jerk to the main pilot but also a sensitive intellectual who loves archaeology.
Gaiking's pilot can be whatever so long as s/he doesn't make Gaiking less interesting. Even Sanshiro was a bog-standard type of protagonist back in his day, so why shouldn't Hollywood get to come up with their own?
Regarding Gaiking Neo not using anything but oblique references to the original cast, I've heard that's because Toei only owns the mechanical designs to Gaiking. Due to a lawsuit, the characters are owned by Go Nagai, so you have to get his permission to do anything with them.
That's the word from the Italian fandom, anyway. I don't know if this would affect the Hollywood production if it wanted to carry some characters over-- certainly SRW has managed to deal with Nagai to get Gaiking into more recent games.
Gaiking Neo was butt, anyway, so I'm glad it's not going to be the last word on the Gaiking license. If this movie actually comes out it's probably going to be a lot better, even if it's not a very great movie.