If a Proxian is made playable, I'd rather it be someone new. Agatio is old and underdeveloped news.
Wouldn't mind a prequel game starring Saturos though.
I agree they could still walk Weyard, mostly because it was Mars Lighthouse and The Wise One was handing out all kinds of Resurrections left and right anyway. I always got the impression that Felix got along well with the Proxians, so if Wise One let him live with the guilt of offing ol' bros it'd be a bit messed up.
Then again, maybe that's why no one has seen or heard from Felix.
I'm definitely all for a prequel game starring Saturos, that is a must.