I clearly got very very lucky in September. Arrived at LGW for the Saturday MCO flight, hand luggage only. It was 4 hours delayed upon checking in (late inbound from KIN IIRC).

Thinking on my feet I asked if I could be moved to the TPA flight as I could rearrange my CDC to collect from there. Was told to go and get a coffee and comeback in thirty minutes when check in for the TPA flight would be closed. I was warned the TPA flight was full but put on standby.

Came back thirty minutes later, told there was a no show on the TPA and was issued with a boarding pass and whizzed through to the gate. Only on walking down the airbridge did I realise I had been given a double upgrade to CW.

Arrived into TPA after a great CW expereience. Logged onto Flightradar to see the MCO left some five hours late.

So it can happen but you have to be very lucky.