If we're talking about new mechs, I think Spax is going to stick with Gion for... well... ever I suppose. Unless the big Defensers "consciousness" can be transplanted into another body. But that would only be a last resort. I like the id a of Spax being a nostalgic.
Anyway, if Gion can be upgraded that's fine and dandy. Above is a link to a picture I think gives me a good visual representation of what a "new-and-improved" Gion would look like. A bit chubby, heavy armor, slow but strong, and keeping as symmetrical as possible.
(P.S. If you get a chance check out Mobile Frame Zero: Rapid Attack. It's a miniatures battling game that uses Mecha made of Legos.
MF0:RA The game is very fun, and it gives me a chance to "play" with my lego collection again. Not that I need a reason. ;-)
Oh, and the pdf rules are free! This game was the very first Kickstarter I ever backed.
I've thought about creating a story-centric game here on GP based on the MF0 world, and using the mech battle rules. Pretty simple stuff. Hmm... Maybe?