I had a somewhat less standard swap recently at SEA: originally a 737-800 to SFO, got swapped to an A319: after boarding we were told that this plane was meant to go to DEN, had boarded, and then deboarded because there was "weather" at DEN and the "radars" had an issue meaning the plane wouldn't be able to land at DEN. (I'm not quite sure what they meant by radars, being mostly clueless about flight technology I'm assuming lack of weather radar means they should avoid places with possible storms, but maybe this was an ILS issue?)

Ultimately we left on time, albeit with a gate and seat swap, the SEA-DEN left 1 hour late (i.e. at the same time as my SEA-SFO left). I imagine this might have caused seat reassignments and IDBs down the line, OTOH both being hubs would probably minimise issues.

// Edit: no idea why the "A319" is highlighted in red, that seems to be some FT magic...