I would argue it would've happened under current Microsoft leadership. The last year or so, all of Microsoft's studios have been heavily hiring and building up. Rare now has the Sea of Thieves sustain and their other team making a new IP, 343 has over 500 people and multiple teams, including their MCC patch and sustain, Halo Infinite development, etc.
Whenever Microsoft approved their Fable pitch, they definitely understood that they'd be bankrolling the building of a new studio, basically. I'm sure it was easier given how Xbox first party studios and budget were managed under Terry Myserson, but if the people at Playground pitched it a year later, I bet it still happens. It's the kind of investment that Phil and Matt Booty are in the market to make.