In principle it could be done almost overnight:
Everyone booked in the J/C/D/R/I bucket is considered in business class.
Create the right-sized cabins on all flights according to the existing algorithm for CE.
Reseat all pax appropriately, using the existing curtain change algorithm.
Deal with any oversells following the capacity reduction using existing algorithm.
Crew follow band 1 protocols that they already know (?)
Update the fare tariffs if desired (J/C/D/R/I fares are already loaded, just need to be re-described as business class)
Some cosmetic changes to ba.com
Give a briefing to the outstation staff on how to move the curtains
Increase catering orders
Anything else?
I estimate at least a year
