I think the spate of airline expansion and recruitment has cleared out the senior GA drives and those companies are finding it harder to replace (and keep) those people. There are certainly examples around of younger drivers getting moved up at an earlier stage but for those companies with contract requirements the task is going to get harder.
This has been said before on a number of different threads but the day cannot be far off when CASA get a rush of blood and realise that 500 command M/E is no longer necessary to command an aircraft above 5,700 kg and airlines will begin to look at training requirements in the light of what they need rather than taking what they can get.
Just because generations of airline pilots have done their "hard yards" in the bush it doesn't mean it has to be done that way forever. Overseas experience is that airline training is a specialised area rather than a follow on from GA with emphasis being placed on multi-crew operation from the outset.
A former QANTAS C & T captain once explained to me that the company did not like to employ high time pilots as they had learnt too many bad habits that were expensive to remove. Airline specific training from the outset would remove such a need without the need to compromise standards.