this bug will track the effort remaining for the 'full fix' as described in https://bugzilla.xamarin.com/show_bug.cgi?id=43566#c15
Update per comment https://bugzilla.xamarin.com/show_bug.cgi?id=43566#c17 (this is now the bug to track the "mitigation" fix).
I have verified on master that the mitigation effort is effective. Prior to the fix the issue was 100% reproducible in my experience. With this fix, I cannot reproduce anymore, I tried opening the designer multiple (~4) times and my already running iOS10 simulator is remaining responsive.
I will again verify the issue on the release branch once it's merged.
Release ID: 602000494
Git revision: f6483f8a1c6d0790f2d8033a7e4d55e09b57a8bd
Build date: 2016-09-15 06:52:55-04
Xamarin addins: 3291a5df0a089370476aa9b24a4d4996e1df5479
Build lane: monodevelop-lion-master
Also verified it with XVS master.
Verified on release branch.
Release ID: 601010012
Git revision: 8c26c5642182bdee0a1a0c976ca456565086212a
Build date: 2016-09-19 10:21:10-04
Xamarin addins: ee95a0d36b72ed02e773710ca124f0fdc53f86b7
Build lane: monodevelop-lion-cycle8-sr0
Fixed in version 22.214.171.1240 (d15-4)
Author: Alex Corrado
Commit: 58f56b5e92aacf0e2421f39dc6a8b9d7f20793dc (xamarin/ios-sim-sharp)
Included in Commit: 1fd75d9ebd78bcbb1de9c6997ed75c949d96085c (mono/monodevelop)