I’m able to build and release an update with Xcode9 and run on ios11.
Xcode9 did loose a lot of my config but opening my xcodeproj file in Xcode and tinkering with things did help.
Despite Xcode showing my signing cert and provisioning profile, I had to uncheck and recheck the little checkbox.
Then Xcode9 requires a 1024x1024 icon now. running ionic resources ios would not generate this, so I made one manually and then opened up Images.xcassets file in my xcode project and dragged the 1024 icon onto the placeholder.
[EDIT]: looks like ionic cli 3.11 fixes this resource issue: Ionic CLI 3.11.0
Built and submitted an update yesterday.