Other folks have done it. The issue is that if you choose an Nexus/Alfine, the gear steps are not consistant (the difference between 1-2 gear is much less than the difference between 5-6 gear). The set-up won't be a half-step, there will be lots of overlap. All you'll do is extend the range 2-3 more gears. If you choose an SRAM im9 hub, the steps are consistant and you can get a wider range with less overlap. No issues on the chainslack, just use a rear dearaillieur...Which kinda defeats the purpose of an IGH....