Would be nice but can't happen as long as the UK is part of the EU, they run our laws, trade and movement policies.
EU would have to negotiate as a whole, at which point Aus and NZ stop wanting it to happen for obvious reasons.
Would much rather sacked the EU off and form a free trade and movement agreement with most commonwealth countries, much more aligned. Less likely to abuse the fuck out of it as well, apart from Aussie bartenders of course. There should still be limits and preferential treatment to skilled workers though, we're mostly islands and population control is essential unless you want ghetto shitholes as the UK is heading. Although a chav community ghetto in Sydney does sound funny.
I've always been a huge fan of the idea of removing borders completely. Bring on the free movement future! They're right. The only thing that truely differentiates us is an imaginary border on the ground we claimed hundereds of years ago. We're all one species, why don't we start acting like it?
Because that is absolutely fucking insane, and people who think that (far too many) really need to think harder on the subject. How do you account for water supplies, food, energy, housing, transport, doctors, nurses, schools, teachers... it goes on and on. They don't magically increase with a bunch of people moving over. Even if you are an incredibly rich society and can throw money at the problem, it takes years to respond to such demand and long term growth planning. You can't just build a nuclear power station when a few million people turn up.