This mac developer preview got released on Monday, during Apples WWDC conference. This version, after many bug fixes and amendments, will be made public later this year, and will be publicly available for BETA in a few months.
When you try to open Minecraft, a dialog pops up which says "'Minecraft' cannot be opened. This application requires the legacy Java SE 6 runtime which is unavailable for this version of OS X". The application cannot be opened. After further research, it appears that Mac has completely dropped support for this Java version. You cannot install legacy Java SE 6 runtime at all.
Thanks,
Toby.