It will work. Google it but Rob english has done it on couple of bikes. It's etube which means almost everything is cross compatible minus 7970 and 6870 WITH 6770 and upgraded battery.
Dropped rob an email and he hasn't done it but says it should be fine as long as you swap out the junction box for the alfine and replace with junction box and derailleur...
He advocates me running alfine 8spd forever and that I'd have no need to return to a derailleur.
It will work. Google it but Rob english has done it on couple of bikes. It's etube which means almost everything is cross compatible minus 7970 and 6870 WITH 6770 and upgraded battery.