My money goes on... Jagdpanther - it may be pure bullish ignorance on my part but there appear to be several things that hint very heavily at it (to me at least).
1) It does appear to be a fixed casemate vehicle - the upper glacis seems to go all the way up the front face & seems a little broad for a turreted vehicle - there's also an artifact that looks like it might be the hull ball mount mg about 2/3rds of the way up.
2) The mantlet appears to be the flat sided pyramidal shape found on the Jagdpanther, (ok - also the first 50 Tiger II's as well, but I've discounted that for the previously stated reason) not the conical mantlet of the majority of the Tiger II production run.
3) The image hints at the rectangular mantlet surround found on the Jagdpanther.
4) The angle of the upper & lower glacis say German (to me at least) - a fairly pronounced point absent in allied vehicles. The implied track sag would also looks fit a German subject (though of course couldn't discount a Soviet vehicle on it's own).
Ok, now i'll just wait (with coat in hand - just in case of a facepalm moment
) till they put us out of our misery.