It will come out with the release of Yosemite 10.10.3 - could that be as soon as next week with the Watch event? We'll see... perhaps the watch event will at least give a date for it.
Is it safe to use as a beta? I think Apple is confident about it since they released it to the Public Beta users on Monday... and if you've got a good TimeCapsule back up to revert to... it should be OK to use.