I don't see it happening Marcel. If it would be possible, why didn't Sony and Canon do it already? Keep in mind that they want to make money as well and they won't do that by just selling camera bodies only. I think if they were going to do it, they would have to set the sensor further back, which would make the camera bigger, which defeats the purpose of a mirrorless camera. The only other option, is to move the lens forward and they have to do that with an adapter.
Well, I haven't seen it happening either, but it would be quite possible. Just think of your adapter as built-in. At least the auto-focus and full aperture metering would be possible.