Unfortunatly, no long glass is available yet for micro 4/399% (or more?) of long lens use is for sports or wildlife. Micro 4/3 isn't quite there yet. The AF systems, while improving, currently isn't suited to this. For example, its very, very difficult to get a good bird in fight shot. Most people who can get a decent shot are using old-school manual focus lenses with adapters. But, the next OM-D should move things up a notch. Panasonic are also promising something special. Following that, I'd be surprised if none of the m43 lens manufacturers (and there are 20 or so companies involved) didn't release a decent 200mm (AKA 400mm) or 300mm (AKA 600mm) lens. After all, the real interest in micro four thirds lenses is in fast primes.
Ignoring arguments about aperture equivalence and sensor noise, an M43 300mm/f4 is going to be a lot more affordable and easier to handhold and use than the Canon 600mm.
I think that cropping in photoshop is cheaper than buying a dedicate crop system just to have something smaller and easier to handhold. For example, cropping (or not) 6D+24-105L images vs. OMD+equivalent lens set (because it is lacking the not-cropping option) - which combo would cost and weight more?