Unfortunately I don't think the issue is going to go away anytime soon. Part of the problem is the differing allowances between airlines in this country. What's ok on one isn't on another- for example you could go with your 10kg's of carry on from Jetstar to a QF flight where the set limit is 7kg (not that it seems to matter much these days!) then Qantaslink which of course is 4kg's for a good reason...
Some pax don't understand that sizes are different for different aircraft too. I personally think the size QF allows is a little too large as that test unit can fit bags which won't fit in certain lockers on certain QF aircraft- have sent in feedback to this effect so we shall see what happens.
Another factor is FF's travelling in economy who mistakenly think their status gives them more carry on piece allowance- it doesn't. I respect that they give the company a lot of business, and if possible allow for suit bags etc, (probably doesn't help) but do explain that it is above the allowance and is only being allowed on today because we have space etc etc and on a full flight it won't be coming in the cabin. Pieces go by travel class not your FF status unless you're a Chairman's Lounge member and even then in economy it's a 'nice to have' when room is at a premium.
Doesn't help that most pax refuse to stow small items under the seat in front. I asked 4 pax to do so the other day and all flatly refused, stating it was 'their right' to use the o/h locker. I understand that but when the flight is full larger items have preference in o/h lockers when they can't fit under seats in front. Eventually I had to ask the people with the large bag to gate check it as we were already past departure time and the situation was going nowhere. Wasn't very fair as they only had the 1 bag between them yet everyone else bringing on their 5 thousand bags meant people playing by the rules missed out.
It's a difficult battle as well with online check-in because now a bag often won't be seen until the pax is at the gate. Then if it's too big we have to hold up boarding while we test the bag, get essential items out and gate check. When ground crew are short staffed sometimes they can't gate check bags, or late boarders come to the gate after loading is finished.
I think it's high time we had standardised limits and have it prominently signaged saying that CASA choose these limits not the airline. I've lost count of how many pax have a 20-something kg bag and say 'Oh but it fits in the test unit!' - it's not just about size it's about weight. I don't think it;s going to get any better until there' blanket rules about baggage- maybe the matter should be enforced at the security checkpoint like they're proposing to do in the US.
Sorry for the long post but as you can tell this issue is one close to my heart!