Xamarin Studio 126.96.36.19941 that is currently in stable is missing the newest simulators from Xcode8.
Fixed in md-addins:master (cbb1fd28d5365d291f4269d90138b0f573702584) and cycle8 PR (https://github.com/xamarin/maciostools/pull/37).
I have verified with on master that the simulators are now showing correctly.
iPhone 7 Plus
iPad Pro 9.7
iPad Pro 12.9
Apple Watch Series 2 42mm
Apple Watch Series 2 38mm
The above are all present and I am able to launch/debug applications on them.
Will verify the bug again on release branch when 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
I have verified this issue with latest C8SR0 XS 188.8.131.52 and observed that all simulators mentioned in comment(2) are showing correctly in dropdown and app is launching/debugging successfully on them.
XS 6.1.1 (build 7)
Release ID: 601010007
Git revision: d8b32f2e91a12d368b5653aa035cde654d38bd53
Build date: 2016-09-19 06:04:49-04
Xamarin addins: ce49b5fab3034cfd40dbb3132d5cf1377e6a82ea
Build lane: monodevelop-lion-cycle8-sr0
Also working fine same behaviour as described in comment(3) with C8 XS Version 6.1.2 (build 3)
Release ID: 601020003
Git revision: 810b88f0ab11307f0258f993e10ec04431aa4036
Build date: 2016-09-19 06:05:39-04
Xamarin addins: 6752c390a3757566d9efef323bbedce1ebaeed98
Build lane: monodevelop-lion-cycle8