According to Ian at Four Thirds User Olympus has made it official that they have gone beyond "determining what could be done" to "working on" a successor to the E-5.

"Akira Watanabe, manager of Olympus Imaging's SLR planning department, confirmed today that the company is definitely working on a body to deliver the focusing performance expected by users of the Top Pro lens series like the ground breaking 90-250 f2.8 fixed aperture zoom."
Olympus confirms new camera body for Four Thirds lenses (Four Thirds User)

I'd guess it will be a mirrorless body that is capable of phase detect focusing. Ideally it would be bigger than an EM5 and use m4/3 lenses natively and 4/3 lenses with an adapter.

Fred