To answer the question, thanks to Theoretical Seating (for which there is a highly detailed other thread) the chances of seating changes are not always good, since in theory everyone has been allocated a seat. Now it is the case that some single travellers try to move around between options, and in particular if they are towards the back of the cabin they may move to a seat further forward. I'm not convinced it's worth the candle: catering starts from the corners and is reconciled in the galley, for example. But after OLCI has opened you may well see some changes. You will also see people cancelling their trip, and last minute booking, which means it's a total lottery. Also note that once you have selected your seats and gotten a boarding pass then it's not possible to change the seat online, it is then a negotiation at the airport (the Engagement Centres usually cannot help once the flight is under airport control). So in short, best to make do with what you can see, unless the seats are totally unacceptable, and then see what they can do at the airport.