Jack looked like a strange idea to me, because all tooling like annotation processing, compiler enhancements (Lombok?), and many others will not work. Javac is great, but it is 20 years old! It would be impossible to create such mature compiler shortly.
Support (and Design, Recycler etc) are very good, but their bugs are incredible sometimes. In support 23.2, IIRC, they suddenly included vector drawables which led to instant crash on Android older than Lollipop. Support-v7 version 24 or 25 suddenly became support-v9 (without explicit renaming), dropping API 7 and 8 support. In support-v13, there is FragmentStatePagerAdapter, which really can be used since API 17, where native child-fragments are supported.
So, in my opinion, Google generates many questions and dead kittens.