Interesting that one of Mr Eddingtons previous employer,- Cathay, which is now reportedly in the market for second hand 744s,- for many years had the philosophy of using old and usually second hand aircraft because their low capital ownership costs offset the higher fuel costs. The same went for " misusing" long haul types on short haul services,- eg 744s on HKG/TPE ( 70 mins), rather than add to fleet complexity by adding a purely short haul type.
This also enables them to get the last few hours of potential productivity out of 744 pilots as well.
On the face of it , using the CX formula, BA would do well to stick with the 744s and wait to see how the A 380 and 7E7 turn out before investing in 777-300s, which if they come in the new LR form will require a reversion to GE engines. The 777 could see a shorter than predicted production run by being displaced by stretched 7E7s, so again wait and see could pay off.
The real case for new aircraft would be if BA were to decide to resume anything more than marginal growth of their ( profitable) long haul business and therefore need a larger fleet.