Maybe something along the lines of party games, with added Kinect functionality. Nothing specific I can think of now, but devs are more creative than I am
On the flip side the PS3 supported 7 controllers (if I remember correctly) and I don't recall any games supporting that many concurrent players.
Technically it was 7 BT devices, which of course includes controllers but they had extra for headsets, remotes etc. The only positive of them choosing that tech IMO; but as you say it was never used for gaming.
Pretty much useless for 99% of the genres out there but if there was demand I could see party games making use of the feature. Unfortunately, MS doesn't really have any IPs in that field e.g Mario Party. I would have mentioned Blitz Games since they made Fusion Frenzy, but well...We all know how that ended this week.