Workaround for this issue until Microsoft adds the target.
- Build your App for iOS Simulator (e.g. iPad Retina)
- Copy the folder platforms\ios (under your project folder) to your MAC development machine
- Open (Project).xcodeproj (inside the ios-Folder) in xCode
- Build your Project for the iPad Pro Simulator and take your screenshots
That did the job for me, hope that helps.