Let me rephrase then, how many bags are you planning to take onboard and how big are they?

If you're taking a small carry-on suitcase and a backpack then you will find most passengers have similar carry-on baggage on QF and VA. You won't have an issue with that, I always fly that way domestically in Australia. You can probably also get away with a small shopping bag or similar on top of that.

Anything more than that is likely to cause you trouble. It will be very visible that you have excess bags, and depending on how proactive the staff are feeling it's likely they may intercept you at check-in, security (on QF), or at the gate. If the flight is full they will be on the lookout for pax with too many bags so they can avoid delays later if the overheads fill up. This is all very similar to the US.

In any case it is difficult to say, enforcement is spotty and inconsistent. If you are bringing the 'regular' amount of carry-on then don't expect any issues. If you are planning to take more than a small suitcase and backpack then don't, just check it in and save yourself the grief.