I have looked at xtracycle and it remains a semi viable option to me. But just the xtra cycle costs more than my entire planned cruiser setup. The other issue remains, you will need a suitable bike to mount it to. The one I have that I considered going xtra cycle with, is marginal at best. (700c wheels, vertical dropouts, aluminum frame) So it may have to wait until I can spring for a the whole assembly, bike included. I really like the ones based on the Breezer...love them internal hubs!
Aaron