I like this somewhat, but the most attractive aspect of it is that there would be a Shimano brifter for Alfine rather than just Versas - which I have, and which work fine, but are just not as nice to use as Tiagra (for example.)

I can see a couple of reasons why this might not work with existing belt-drive frames. Looks like the "module" on the drive side moves the sprocket inboard (assuming spacing stays at 135mm, of course it's a problem if it doesn't, too.) which would mess up the chainline - and for a belt this needs to be straight within 1/8". It's also not clear if a Gates sprocket would fit in the space available either - it has an outside flange which doesn't interfere with the existing Alfine shift cable interface but really looks like it would cause problems here.