True, but I personally believe this is the first step to adoption. The whole issue was around licensing..not because the Hotspot vm had something fundamentally missing (zygote and MVM notwithstanding)
That's hard to know and I have no insider knowledge.
From the outside it seems like a lot of work.
Firstly HotStop is not optimized for fast startup, small footprint or short GC pauses. There is talk about merging the Java ME VMs but such things usually take years.
Secondly Google built many proprietary extensions, eg DEX. I'm not sure that ART can even execute Java bytecodes.