Pentax original SR system can move the sensor in three directions: vertically, horizontally, rotationally.
http://www.pentaximaging.com/files/scms_docs/SHAKE_REDUCTION_FACT_SHEET.pdf
Pentax newer SR system can move the sensor in two directions: vertically, horizontally
According to this K-x descriptions below, it appears the K-x may be using the newer SR system and the K-7 is using the older type.
"Like almost all shake reduction systems, the Kx's shake reduction can correct only for horizontal or vertical motion, but not for rotation -- a rare capability that is offered by the K-7."
Pentax K-x Digital Camera - Hands-On Preview - The Imaging Resource!
But I think the newer SR design has the advantage of being able to support a large/heavier sensor. So there may still be hope for either a 645D or FF in the future. At least, Pentax now has a SR system that can support it. Otherwise why would Pentax spend money on a new totally redesigned SR system when the original one has been working fine for aps-c sensor?? Since SR makes more sense for a FF than a MF as no current digital MF has build-in SR, if I have to place a bet, I would put my money on a FF.