Just randomly checked some upcoming flights and a few plane / seats changes, not all for the best.

My LHR-IAD on the A380 is fine at present.

A LHR-JFK flight has changed from a 747 to a 777 and my usual Y seat was taken so had to grab a middle aisle bulkhead instead. Now I can get my usual seat position (probably right next to the toilets now which may be better or worse than the centre aisle seat half way back down the plane they changed me to)
Expecting AA to change my return flight at some point as they always cancel / change times etc.

A LHR-AMS flight has now changed aircraft and handily, the exit rows I couldn't get in ET as they were taken / blocked are now free so I've got my favourite window seat now

Did have 1A booked in First on a 747 LHR-JFK and that's now changed to a 777 - not sure whether to stick with that seat in case they change back again. Was really looking forward to being in the nose.