You can run an IGH on a bike with vertical dropouts without having to use a chain tensioner. Eccentric bottom brackets can be purchased by companies such as Tr!ckstuff, Forward Components, and Niner Bikes. There is also a bottom bracket chain tensioner by Yess Labs that offers a different solution. If you don't mind using a traditional chain tensioner then I second the above suggestion of running a front derailleur and double chainring to give you the extra gears; just like the Jamis Commuter 4. Personally, I like the clean look of no derailleur and I am very intrigued by the new 11-speed Alfine hub. At a third the cost of a Rohloff and with over 400% gear range it should be a winner.