Ask Square Enix first !
I am sure that is a significantly smaller hurdle to jump than actually getting the project off the ground. Larger hurdles would be Takahashi wanting to take on such a project, and that hurdle is directly linked to the actual scope of a remade Xenogears would dwarf FF7 remake in terms of content volume. Especially considering Takahashi would no doubt wish to put in open world elements (if not make the game an evolving open world/ traditional RPG hybrid).
As well, Takahashi has no need to ask Square Enix if he can teimagine his own story under the Xenoblade Chronicles X banner as long as he doesn’t violate any trademarks; he’d even be able to reuse certain names (as he has done in the past) if he wished.
It is, unfortunately, unlikely Takahashi would want to redo a project on the scale of a modern Xenogears because of the scope. But I can always hope =)
I describe myself as a little dose of toxic masculinity.