It would be very risky for BA to develop a 3-4-3 program for the 777 knowing the history. Most likely they would trial the configuration first with an off-the-shelf seat like the Recaro BL3520 or something like that.

This way the time from ITCM to delivery will be much less than a custom program.

If there is a trial for one year and then another two years to finalise the bespoke BA program we would potentially have three years' warning.