upgrades
Goeasy,
I dont think the issue is about whether a new upgrade can handle a cadet. (For the record, by the time they are signed out on line, they are no longer cadets.)
I think the issue is rather about experience levels. There have been some high profile accidents in the past, where pairing 2 inexperienced crew were cited as contributing factors. ( Potomac accident and GF 072 spring to mind) I would think that there are insurance issues here as well as rostering difficulties. (However, with a decent rostering system, this should be taken care of.)
I think the better option would be to upgrade on the A320 and put the Second officers on the A340 as in flight relief for a year or so to give them exposure to the operation, before they gotta worry about flying the Bus.
But what do I know anyway??
Sir O