I live in Canberra (lol), car is still registered in NSW after 8 years - I have to drive a whopping 20 mins to Queanbeyan (more lols) to get a NSW rego check done - thou there is a few places that can do NSW rego checks too.
I didn't change my license over for 2 years or so (basically till it ran out) and the RTA here didn't care.
I've run up the back of a Honda a few years ago, insurance didn't car - no popo involved.
I've been pulled over a few times for speeding/RBT/WTF is with your car (both with NSW and ACT licenses) and no-one said anything about what state the license was/wasn't in.
Only time it was an issue was when I got defected (well my wife did...) and the 5-0 couldn't work out about the different name the car is registered in (a business name).
So basically, no-one in ACT gives a fork about it.