I upgrade to Yosemite my Mini Mac (yesterday) and after a long hours (almost a day) the installation was succeeded.
I enter in my source code in Xcode 6.0.1 and afte
In Xcode 6.1 you can add simulators manually. To do so go to Window -> Devices and press the + symbol left at the bottom.
Then you can choose a combination of device type and iOS version to create.
if the iOS version you wanted is not there you'll be ask to download more simulator and directed to Xcode->Preference->Downloads.
Note: you can directly go to Xcode->Preference->Downloads and download more simulators and it will automatically available in simulator list after download.