Tom,
Great question.
We have been testing with iOS8 internally throughout the iOS8 beta release cycle. Things are looking really good and Explorer will work on this platform. Since iOS8 is still not officially released we can not certify on that platform or build the app with the new version of XCode. With that being said, we will be adopting iOS8 as soon as it is officially released (Sept 17th I believe).
You can expect a release shortly after iOS8 goes live where we officially certify and build on iOS8 but if you want to start using iOS8 sooner with the existing version of Explorer we do not expect any major headaches or stability issues.
Hope this helps,
-Brent
PS did you see the Apple product launch/presentation on Tuesday ... exciting times ahead.
