Alfine is great, but you'll need a chain tensioner to run one on a G Spot (as you probably already know) because despite the BB main pivot it only has conventional vertical dropouts…
Test rode a G Spot a few years ago myself, found it to be susceptible to pedal induced bob more than any other bike I'd ever ridden! I'd suggest that due to the Alfine essentially requiring you to get out of the saddle and crank a bit harder (not as hard as on an SS) due to lack of such low gears as with a full 27 speed setup, it is far from an ideal combo though! Alfine hubs work superb on hardtails, I'd consider running one on a short travel full sus that pedals efficiently, but due to weight and increased pedalling torque required wouldn't want to run one on a long travel bike that bobs a lot.