is it possible to do?
No it's not as has been stated before on the forums..
Maybe in future releases although i do hope so.
As Ray mentioned, it is not possible to migrate AppStacks from 2.x to 3.0. This is mentioned in the release notes VMware App Volumes 3.0 Release Notes
There will be a migration path from 2.x to 3.x but not for 3.0.