Had a Skywest flight that was originally scheduled on a CRJ. Got an equipment swap to an E175, so that's already an upgrade.
The F inventory never populated, and the waitlist was empty.
I inquired at the gate, and the gate agent told me he wasn't sure if the system would let me upgrade "officially" but that he'd cleared it with the cabin crew and that I could sit up front. It seems that he then called up one other 1K and a GS and told them the same thing, because the flight ended up with 3 up front, 9 empty seats, and no (official) list.
It probably would have cleared all the way down to Silver if they'd run the full list. Luckily it was a short flight, and anyway if you book a CRJ and you get an E175, I doubt you can be
too upset. But I'm still glad that I asked.