Brilliant! I've thought in the past (based on other builders inputs) that the outrunner inside the geared hubs was a great size for BB-drive. I haven't had the time or money to play with one, and based on the pics you've posted, you are just the builder for the job!
One of the reasons this is a great idea is that the cell_man MAC geared hubs can be had in 5 different Kv's.
edit: heres the ES list of geared hubs viewtopic.php?f=3&t=4892
Golden Motor MBG36