Want in? https://www.atlassian.com/company/careers ;) When a company has had 30% growth per year according to their F-1 filing (This is a ballpark - please check the filing), you don't need to wait to get hired. More seriously, in a Forbes article last year Scott Farquhar said some employees would be able to buy a house, so there are probably some people who want to pursue some personal projects. I expect Syndey real estate to become very expensive, but I also expect such companies to have some retention policy, like progressive vesting and post-IPO lock-in period.
And now add earnings to that and Sydney is not that expensive. Pure price per m^2 says nothing, the important thing is how much m^2 I can buy with my average salary.