Ultimate, yes, to me though it might seem a bit overkill. I am glad my Xtracycle has a 7-speed internal hub. But if you insist on low-gravity in the front, here's the American version that would certainly mate up with an Xtracycle. I believe Worksman can configure just about any hub you would want on the rear (except maybe they don't stock Rohloffs
If you insist on carrying the big loads up front and in back, Worksman has something there as well...
Lots of options for configuring Worksman bikes, and always a fun site for the cargo-bike minded to visit:
Worksman Bicycles