Try run with terminal , $ appium
And then click on inspector.
This was my situation
macOS Sierra version 10.12(16A323)
Appium v1.5.3
Xcode Version 8.0 (8A218A)
and the solution worked fine,
https://medium.com/@chenchaoyi/the-options-of-inspecting-ios-10-app-with-appium-1-6-534ba166b958#.82oqogqhp