Originally posted by Not a Number That's what Canon did with the EOS-M. There are 3rd party adapters out there for other mounts. I don't think the EOS-M made much of a splash market-wise.
FWIW Canon said at Photokina 2014 that they are "really focused on mirrorless and we’re spending lots of time, and devoting a lot of manpower to scaling up mirrorless development right now."
Since I currently have a Canon Rebel, I looked at the Canon EOS-M, which is basically a mirror-less variant of the current Rebel, before I settled on the Pentax Q7; there was nothing to distinguish it from the competition, apart from the fact that i could use my current lenses on it (with an adapter). Unlike its competitors, it does not have an EVF, for example; I was willing to get an enlarging hood for my Q7, because it gives me the advantage of going after super-telephoto pictures, but I didn't see any reason to do that with the EOS when I could have a Sony A6000 instead. I think Pentax would have to face the same market realities if they came out with a mirror-less variant of a K-5/50. That is one reason I think it would be good for Pentax to develop an add-on EVF for the next member of the Q-family; it would provide all the experience they needed to create a competitive mirror-less K-variant if the market does make a hard turn towards mirror-less in the APS-C sector.