In case there is still time, anything having to do with stereoscopic 3D shooting, such as synching of two cameras (i.e. having one lock ISO/Shutter/etc and drive the other, besides "synch lock", of course), would make it more appealing to me. I already wish they had designed it with the lens as close to one side as possible instead of in the middle of the camera as to use two together side-by-side for 3D, etc.
But yeah, IS support on Canon EF is desirable.
As is ANY other frame rates that can be supported. I.e. no shame on supporting something like 34fps if that's the most the camera can do. I just never understood why it must be only "standard" frame rates that are supported when both, there are so many "standard" frame rates (23.9,24,25,29.7,50,59.7) and so many that are not even standard (30,48,60). A well designed firmware/hardware, specially in a "RAW" camera, should allow for just about ANY frame rate from say 1fps to say 32fps. Your choice. Something is better than nothing.