Above everything else I'd like a 23/2.0 built to the same size as the planned 35/2.0 WR. A 16/2.8 or /3.4 appropriately scaled down in size from the 16/1.4 would be great too. The /1.4 lenses are great optically but I'd very very happily trade a bit of light gathering ability for smaller lenses. Especially with the size reduction in the X-T10 the proportion of lens to body in the X series is getting out of balance IMO.