UA1115 downguaged from 739 to 738, taking 4 F seats with it. UA app offered me a $100 ETC which I did not take. After UA called me, got rebooked onto the direct TPA-SFO flight and a $400 ETC.
This is one of those tough situations where you have to ask whether it's better to just take the $400 and run, or to stick with the flight for a much higher offer at the gate. Even if they found 4 people in F to switch flights, Y is still oversold by 15+, and vouchers will likely be pretty hefty to bounce at the gate.
Nonetheless, $400 for a proactive reroute onto a direct flight is a good deal any day. Nice catch.
BTW: Keep an eye on your new flight... betting that one will end up over by a few as well from those rerouting off the downgauge that are headed to the west coast.