Now that SimCity has fixed most of the launch issues and even added Cheetah Speed back into the game, EA and Maxis are expanding onto a second platform. The game will hit Mac on June 11, exclusively as a digital release.
If you've already purchased SimCity on the PC, either as a physical or digital copy, you'll be able to download the Mac version for free as well. All future purchases will also be cross-platform. You can also access your cities across the two platforms, if you're switching back and forth for some reason.
SimCity was originally planned to launch on Mac alongside the PC version, and EA promised cross-platform functionality at the time. But when the game was delayed it apparently bumped back the OSX version even further. EA is making good on the cross-platform promise, though, so better late than never.