Not that I'm saying there's anything wrong with that - nice to see him actually develop games again, instead of just supervising
How do you define "develop"? Sakaguchi's role today isn't too different from what it was during his later days at Square, specifically during the production of Final Fantasy IX (and the second half of The Spirits Within).
As has been described, Sakaguchi's primary residence is in Hawaii, where he writes scenarios and designs game concepts. Once that initial document is finished, a project is (for all intents and purposes) out of his hands from a creative standpoint. The production studio (responsible for turning that design concept into an in depth work, followed by production) takes over, and Sakaguchi's role becomes a supervisory one.
[according to Microsoft and Feelplus staff, supervision on Lost Odyssey involved meetings with the team twice a month, during which he'd provide feedback and/or ask for specific changes]
FFIX worked the same way, with the Square team filling the role of the development studio.
MistWalker sounds like a funky new company
Well, Mistwalker is a concept design shop (one concept creator, three business folks who manage his office) rather than a game company in the traditional sense. Whether a game turns out great or merely okay likely depends on the competence of the production studio (Racjin, Feelplus, Artoon, Cavia, etc.) and the publisher's commitment to quality.