I use PM extensively in my work flow, but still wonder why there is no arbitrary rotate feature. I heard that this may slow down PM too much for many people, so therefore I was thinking why don't CameraBits supply an add-on light weight edit app, so when you want to rotate, or maybe do a little more work to the photo etc it launches this standalone add-on app and allows you to do this and then take you back into PM with a new file, not to dissimilar to LR or Aperture, but instead this is aimed at immediate editing needs. The new file created should be marked appropriately of course!
This would allow the speed of PM to remain unchanged and allow you quickly to edit a bit more than at present, it would be fast and quick with the basic useful tools you need without having to just use PS or other over weight applications in the launch feature with PM.