This might be rarely used operation for digital camera images, but not so for film scans for example. And the fact that you can not tell if an image has been L-R flipped or not is very disappointing.
You got my vote. One of the reasons it's not in the edit history, is that it is handled very differently than other edits, internally, and requires special handling everywhere it's handled. I'm sure there was a reason why it was done the way it was done, but I too would love if it could be handled just like any other edit - history, and all...
A workaround for the mean time: load xmp sidecar into a text editor and inspect orientation there. If you're a DNG'r you'll need a hex editor, or exiftool, or xEmP.
PS - It's presently missing from both dev-settings and raw-metadata, so plugins can only get at it via xmp or sql. - this I'd like remedied as well.