No, OnePlus still doesn't support the Australian market at the moment. I've not had problems with the OnePlus phones (I even got my mum on one...) in Australia, but they don't officially sell it there (gray markets do work...) and the telcos will not know what the hell the phone is if they need to do support. There are sometimes some band issues, but mostly it is okay.
I think part of their cost savings (from the old days at least...) was the grassroots guerrilla marketing (with low marketing costs)... and the highly target distribution to areas like Europe, India and places like that... avoiding the highly saturated Western (US, Australia, UK) markets that were already dominated by Samsung and Apple. This meant that they didn't have to load up on marketing and subject their phones to "partnerships" to just get noticed!
I've been with OnePlus since the Nexus line went belly up (the first OPO phone, with the invitation to purchase)... the OnePlus phones always offered great flagship hardware at cheaper prices, which always appealed the nerd in me! However, over the last few launches, the prices have been steadily increasing (not as bad as Samsung and Apple flagships... yet...) and that really started to irritate the OG community. Anyway, with the NORD, they have gone back to the original philosophy with decent specs at lower price points. This year, they are up against the Pixel 4a (which you CAN buy in Australia).
So, partly brand loyalty... although, I will have to see how this system UI change and the "partnerships" play out. The Pixel 3a/4a lines are less packed with internal goodies... but they have that awesome Camera software... I have my wife on a Pixel, she prefers the quality photos rather than the speed, storage, multi-SIM, high refresh screen and stuff like that!