I have been given keys to a different room on arrival a couple of times (same hotel): "The room you booked isn't ready now."
I have been upgraded from my selected room once, by the clerk on arrival; however, I suspect he was doing it for a reason unrelated to Diamond. Otherwise, I use mobile checkin generally at properties where I'm fairly certain I'm not going to be upgraded ahead of time.
On a related note, I tried digital key first time recently, which was good for bypassing checkin, but as a key itself I found it clunkier than a plastic card.