Yes, we had it happen once. Moved from inside to outside, but it was a last minute booking and I think they just put us anywhere available to fill up the ship. We've never tried upgrading once on board so not sure how succesful that might be.
I've never had it happen,,,and we cruise A LOT! I've been upgraded many, many times, but when the docs arrive, they have the cabin number on them, and that's pretty much it. I've noticed that lately, the ships are at capacity, so even if you wanted to pay for an upgrade after arrival, you'd be out of luck. FULL SHIP! I'm sure the "upgrade upon arrival" does happen, but I have to believe it's extremely rare.
We sometimes book last minute guaranteed cabin. We then don't know our cabin until we get to the ship. Porters have to look us up to know where to send the luggage. But, once a cabin assignment is given, not likely to change.