Right now when you don't have provisioning profiles set up for your extensions you will get an error like:
However, it's perfectly fine to use a wildcard app id provisioning profile for both the app, watch-app and extension.
My suggestion would be to maybe warn, but still continue and use the provisioning profile selected for the app for the watch-app and extensions as well.
For sample apps e.g. then all we need to ask is for them to add the Apple Watch to their wildcard, if they haven't already done so. Instead of giving them the impression that they need to go through the hassle of creating all these profiles and adding them to tiapp.xml.