As to BA taking any more 380's, why buy new now when in not many years LN 30 and above frames will be coming off lease. If RR's, the PIP improvements could be introduced, a decent improvement.
BA have a number of 747's (somewhere in the mid-teens) that they intend to withdraw in the mid-2020's that currently have nothing on order to replace them with. I get the impression that the A380 is something Willie Walsh would like to replace some/all of these if a deal can be made to match his pricing expectations. After all, LHR is the perfect airport for the A380 (let's put the third runway to one side as that's at least 10 years away and has a long way to go before there's spades in the ground). It's probably getting to the stage where a decision would need to be made soon to secure suitable production slots for whatever they choose that fits in nicely with these timescales. There's also likely to be competition from whatever BA chooses to replace the older variants of their large fleet of 777's, some of which will be approaching 30 years old during the second half of the next decade and they have previously indicated their current thinking is to retain 777's for 30 years.
You're also assuming that enough A380's will be available for lease by then as there's nothing to stop the existing airlines extending leases if they see fit to do so, plus any that do come off lease may not be suitable for a whole host of reasons (cycles, engines, condition, work/money needed to reconfigure them to BA spec, etc.).
Of course, if there's a steep recession in a few years time and BA decide to make cuts in response, they could simply replace them with nothing and order something smaller if/when things pick up again.