Personally I think the best option might well be to wait for awhile and see whether we get a FF mirrorless released by someone like Canon or Fuji.
Waiting to see what the competition will come up with could have you waiting for ever as there will always be something new around the corner. I can't see Canon getting into a FF mirrorless system very quickly since they don't really have anything similar in APS-C to build on yet. Besides, they're doing very nicely thank you with their current DSLR line-up. It is rumoured that Sony's planned upgrade to the A900/A850 FF models in 2012 will be another SLT, the A99, with a possible Nex-9 to accompany it. But I wonder whether mirrorless FF is a good idea anyway as lenses will have to be bigger to cope with the increased focus area. The shorter focal plane distance adopted by Nex-3/5/7 might not be sufficient to avoid distortion at the edges so this distance may need to grow. Added together it all gets a bit cumbersome.
I think shutterless sensors will be the Next Big Thing.
