As with every new major version of iOS we are fully committed to support it. There are a couple of things that should happen before AppBuilder releases an official support for iOS 9:
- Apple should release the official release (aka golden master)
- Cordova should provide support for it.
- AppBuilder should be updated (all AppBuilder clients and AppBuilder cloud infrastructure) to use this new version of Cordova that works with iOS 9.
Judging by past experience it took Cordova 1-2 months (from 17 Sep 2014 to 06 Nov 2014) to release support for iOS 8. AppBuilder releases on a regular cadence of 6-8 weeks which yields that in late 2015 full iOS 9 support is expected.
Note: Apps built with AppBuilder will work in iOS 9 without any modifications because Apple guarantees backwards compatibility. However if you want to take advantage of some iOS 9 specific feature you will need the AppBuilder support to be in place.
Hope this helps.