Gates belts are really just a matter of mounting a different drive sprocket.
There is compromises with them though - they are less efficient than chain, and need a lot of belt tension (rear of bike needs to be quite stiff to prevent flex and potential tooth skip in SS or gearbox hardtail applications). In theory the belts shouldn't cooperate with the reverse bending round a tensioner, but bikes like
@Zaf's Nicolai prove otherwise so that's something of a paradox. Also some users report poor cog life in gritty conditions.
If you're bothering to design an efficiency-focused gearbox like in Shimano's design, belt wouldn't really make sense IMO.
While I'm being negative - I really doubt Shimano would ever bring this design to market for "analogue" bikes. It looks like it's designed for (A) locking up the tech under a patent before anyone else gets a chance, and (B) adaptation to e-bike use to create an integrated motor/transmission unit. It would be equally marketable for urban and mountain biking in e-bike form (the bikes are generally hideous already), but I just dont see the benefits for a "analogue" bike.
If you're going to kill the cassette and derailluer, a casette in a box - and still having to ramp through gears - doesn't interest me. I'd rather loose a couple of percent pedalling efficiency and have instant shifting from true gears without having to have a direct driven (fixed hub) chain or only shifting while pedalling.
IMO, Pinion has made the best bike gearbox so far - but has a way to go yet. A Pinion style box with the ability to be integrated into the frame like the side-plate bolted to frame design used on Cavalerie/Effigear bikes to save weight, and replacing Pinion's low-engagment internal freehub with a sprag clutch or high-engagement ratchet would be two huge improvements to their current designs.
Truth be told though - I prefer the Effigear design overall for it's simplicity. Just a shame it's a little gear-range limited compared to the Pinion boxes. And after playing around with linkage designs the last few weeks - the Effigear offset output shaft is a real PITA in linkage packaging terms. If Effigear did a box with an additional 'speed' added and a concentric output shaft (a la Pinion) that'd be the duck's nuts IMO.