I would also expect you have a good chance of seats opening up but just for a little perspective there is nothing available for mid-September through January 2018, including the last dates that have just opened up (except the Christmas week). Unless you looked but passed earlier, I would think there was never anything offered, rather than you having missed the opportunity. Unlike CW, BA don't guarantee to open up any F seats initially. The implication is that waiting for the spring to open up is no guarantee either.

There is good availability for this spring and summer (2017). That would hint towards you having a good chance, but if you want to secure something have you thought about an earlier, rather than later, trip? There's also decent availability on the LCY CW service if that has any unique appeal of its own to you. If you booked either of these plan Bs you could change date/route/class later (for a fee).