I bought the update off the App Store last night and have been running it (admittedly plugin-free) with no issues for a couple of hours. It is remarkably faster than my previous method of using a Bootcamp install to run it in Windows, plus there are no weird hardware issues with having to turn off multi-core processors, etc.
The graphics have a native resolution setting that matches my monitor (2013 21.5" iMac/Mavericks/Fusion Drive) and they are running in hardware mode at the highest settings. Regions and cities feel like they load almost instantly compared to the Windows version on the same machine.
Tonight I will likely cruise around to find some plugins to add to the install and will post again if I run into any issues.
This is some of the most exciting news regarding SimCity that I've seen in a long time. The debacle that was SimCity (2013) nearly ruined me on the franchise.