Personally I cannot believe it is a permanent move. Cadet schemes at EasyJet and Ryanair are beneficial to the airlines. They provide a stream of qualified people who they can pay less than an experienced pilot. The A321 issue is a red herring. The rules have changed to say that cadets with less than 6 months experience cannot land the A321. All that means is that they are pilot not flying for that sector.
I'd agree with that. The inefficiency in rostering for 6 months if cadets can't operate the A321 (or at least can't operate significant numbers of sectors as they would have to be PNF for all of them) is surely outweighed by their lower salaries. And a lot of cadets go to LGW where there aren't any A321's anyway...
What I fear is that the delay is actually due to costs or Brexit fears. BA has one of the better schemes out there at present for cadets with the bond repayment, loan guarantee and relatively good salary on offer. I hope to be proved wrong, but this could be the new chairman's famous cost control having an impact