I would imagine there would be ways to secure sufficient supply of instructors if you possess they key to something they want.... e.g. an airline job after a couple of years instructing.
They could also possibly retain some of their graduates, put them through an instructors course with the “reward” of a better opportunity - e.g. straight into a jet rather than a turbo-prop afterwards, and a frozen seniority position.
That wouldn’t solve the issue of senior instructors and examiners, but simple $$$ could fix that.
Don’t forget, both VA and QF are doing this mainly to ensure pilot supply for their lower-paid subsidiaries, not so much their mainline jet operations. Mainline jet jobs will remain a large carrot if they need one.
As for standards, if the airlines have a vested interest in the quality of the graduates, this should be good for training standards shouldn’t it? Why would they want to churn out poorly trained pilots? Of course this may depend upon the terms of the contract they have with the contracted training organisation, and whether the airline maintains any involvement in the training and standards, and perhaps who foots the bill if a student needs extra training to meet a standard.
They would also get to choose the applicants. Any mug with $150K can do a CPL course, only to be told at the end of it that they are unemployable by an airline. Wouldn’t it be better to be told beforehand that you would never stand a chance of a job with an airline?
I also doubt that this will become the only route into the airlines. Why would they close other doors? It is very healthy for an airline to have a range of backgrounds in their pilots. For example, I just found myself considering the range of backgrounds in the QF management. The current head of training is ex-TN, the previous ex-Military, and I think the one before that may have been a cadet. People are people, whatever route you have taken, there will be a range of candidate quality.