I did follow most of the advices here without any simulators working.
I had to remove a single simulator to get them working again.
prompt> xcrun simctl list
== Device Types ==
iPhone 4s (com.apple.CoreSimulator.SimDeviceType.iPhone-4s)
iPhone 5 (com.apple.CoreSimulator.SimDeviceType.iPhone-5)
iPhone 5s (com.apple.CoreSimulator.SimDeviceType.iPhone-5s)
iPhone 6 Plus (com.apple.CoreSimulator.SimDeviceType.iPhone-6-Plus)
iPhone 6 (com.apple.CoreSimulator.SimDeviceType.iPhone-6)
iPad 2 (com.apple.CoreSimulator.SimDeviceType.iPad-2)
iPad Retina (com.apple.CoreSimulator.SimDeviceType.iPad-Retina)
iPad Air (com.apple.CoreSimulator.SimDeviceType.iPad-Air)
Resizable iPhone (com.apple.CoreSimulator.SimDeviceType.Resizable-iPhone)
Resizable iPad (com.apple.CoreSimulator.SimDeviceType.Resizable-iPad)
== Runtimes ==
iOS 7.0 (7.0 - Unknown) (com.apple.CoreSimulator.SimRuntime.iOS-7-0) (unavailable, runtime path not found)
iOS 7.1 (7.1 - Unknown) (com.apple.CoreSimulator.SimRuntime.iOS-7-1) (unavailable, runtime path not found)
iOS 8.1 (8.1 - 12B411) (com.apple.CoreSimulator.SimRuntime.iOS-8-1)
== Devices ==
-- iOS 7.0 --
-- iOS 7.1 --
-- iOS 8.1 --
iPhone 4s (5F44F3AD-FE17-4EF6-A8DD-5A10E2EDCA09) (Shutdown)
iPhone 5 (76053A14-F43C-4A32-8A72-96177C848741) (Creating)
iPhone 5s (7998167A-E763-42F6-8945-65B514378154) (Shutdown)
iPhone 6 Plus (4360DA62-2C1E-4529-AA30-F11CC9357854) (Shutdown)
iPhone 6 (EE992AE3-B08E-4897-B28D-CEA486062E05) (Shutdown)
iPad 2 (0D28BB5D-DD40-419D-8BA7-E9A1E9C777C6) (Shutdown)
iPad Retina (365413A3-3F93-4EC4-B2DE-0D65358A81F3) (Shutdown)
iPad Air (13CCAAF0-268D-47B0-9031-2034BE919BC1) (Shutdown)
Resizable iPhone (8D5A265E-B714-4298-988C-3365E18391C9) (Shutdown)
Resizable iPad (0EBB1D3B-951C-4BB1-813B-A0E83E67B0EB) (Shutdown)
prompt>
Solution was to delete the simulator stuck in (Creating) mode
prompt> xcrun simctl delete 76053A14-F43C-4A32-8A72-96177C848741