I have seen quite a few belts on internally geared hubs - a quick search turns up quite a few[1] commuters shipping w/ belt + Nexus internal hub.

1: https://www.bikeexchange.com/blog/best-urban-belt-drive-bike...

Absolutely: internal gear hubs are the only gears you can use with belts. They just tend to be substantially more expensive for the same amount of gears as a comparative derailleur. Internal gears also tend to have a higher friction than derailleur gears - the really good ones such as a Rohloff speedhub cost > 1000 EUR. Even a comparatively mundane Alfine 11 gear costs ~ 400-500 EUR. A pinion gear isn’t exactly cheap either.

In return you get a mostly maintenance free setup. It’s great, but I probably wouldn’t opt for it for a city commuter bike.

And most belts are a permanently closed loop, unlike chains which can be opened and closed. This means you need an special frame with an openable rear triangle.

It doesn’t actually need to open, but the frame must be built to support belts. The lower bar of the rear triangle must pass over the belt.

Interesting comments about the suspension. Several models of motorcycles use belt drive and they have both front/rear suspension.

BMW uses them on some of the F models, Buell’s where all belt drive and I think all Harley’s use a belt transmission.

There are plenty of motorcycles with belt drive, the suspension doesn't seem to be a problem.

motorcycles have different issues. The gear changes are internal inside the transmission, not in the belt drive line. Also, bikes tend to have multi-link suspension with chain growth through the travel. This allows the suspension to be reactive to pedaling forces to reduce rider induced pedal-bob that eats efficiency.