I'm not understanding these reasons
Will Google do this? I don't know. I don't understand the reasoning why they would though:
1) The "API" argument. OK, so Google ends up owing billions to Oracle. a) Would changing anything in 2017 affect those damages anyway? b) Are they going to rewrite an entire new API from scratch then? In one year? Keep in mind, they can't just "close source" the same API -- they still will be shipping an implementation of it, which I assume would be enough to get them in trouble with Oracle anyway -- and if a judge is stupid enough (hey judge, if you decide this you are STUPID!) to decide API itself can be copyrighted (so you can't clean-room implement it...) then, well, you can't write Android software without an API of some kind. So they can't just close source the existing API and have this actually help anything with Oracle.
2) The "faster updates" argument. a) Many many phones, the vendor simply does not bother to do anything in terms of updates; either they ship none, or maybe a minor version update, like "x.y.0 to x.y.2". I simply do not see how it being closed source versus open source helps this in any way; many vendors simply can't be bothered to release updates at all, and in other cases, they do some nasty things ^H^H^H^H customizations to bring up Android to begin with, and don't want to have to do it again to make it run on a newer Android version (the first couple LTE-supporting phones I had had this problem... Android didn't really support LTE yet, so the data support for switching between EVDO, HSPA, or LTE was like some vendor-custom hack that would then have to be reimplemented from scratch for each new Android version.)
3) I'm just not seeing the advantage. If they are not having problems (businesswise) of vendors taking base Android and putting their own stuff on top, then what's the difference if it's closed source? It'd be a lot of trouble to reimplement for something that's not causing Google a problem.
4) Tweaks and optimizations? This argument just made no sense to me -- if you want people to find little tweaks and optimizations and improve your code, to improve battery life, and so on, closed source is not the way to do it.
5) I'm ignoring the "people want Android because it's open", "don't be evil", etc. arguments, I don't disagree but others have covered this argument more eloquently than I could.
On the other hand, I can see wanting an ART that is not dependent on AOSP -- you see this with Cyanogenmod, on some phones where they can't get a rebuilt kernel onto it... the Android userland will be pretty specifically tied into a certain kernel version. For instance an old phone I had, you could get a CM7 onto it to upgrade it from 2.1 to 2.2, but that was it, newer Android runtime would not work with that kernel. It would be nice if a newer userland could run on an older kernel, and could help some phones that do not get updates otherwise to at least be able to get a 3rd-party update (i.e. Cyanogenmod) even if the vendor doesn't release one.