No way, no how, could the replacement 7D be a mirrorless camera. That would kill it for 95% of the users.
Like it or not, mirrorless is the future. For one BIG
reason, cost. An EVF cost less money for the camera companies to produce. Less cost
= more profit
, simple as that. BTW, this is also the reason why menues are replacing analog controls.
Hard to tell what a Canon or Nikon DSLR replacement will look like. My guess is Nikon will go for a Sony SLT style camera, (with an F-mount), and Canon will do something radical (and replace the EF-mount). Remomber that Canon replaced the FD-mount with the EF-mount, when they went to auto-focus (it could happen again).
The question is not if
it will happen, but when
it will happen.