What I was hoping for has happened. All free coach seats have been taken so only MCE seats are now available. I checked in on the AA app and have been assigned 15A which is good because I wanted a window seat. From looking at seat guru it appears this is one of the MCE rows without AC power which I would have preferred but u don't want to push my luck by fiddling around to try and swap at this stage.
I don't seem to be able to get my boarding passes within the app, I'm wondering whether this is because my last connecting flight is more than 24 hours away. I'll try again once I'm within 24 hours. I like using mobile boarding passes as I find it easier (and also like to collect them on my phone) so I'd prefer them to getting paper ones at the airport.