I am looking for info on whether OAK's CompositeNodeStore is available in AEM yet. I would like to do a POC of running AEM in Containers / Docker for a blue/green deployment similar to what was presented at AdaptTo() 2017 and found questions answered last year with a consensus that Oak 1.8 was required and not available in AEM 6.3. I am currently migrating from AEM 6.2 to AEM 6.4.3 with Oak 1.8.9 - is CompositeNodeStore available yet? And is there any current documentation on that option?
It is not supported. You might try it on your own, and you might get it working, but I would not recommend it for any production setup.
Also, if you are migrating from an older version, make sure that you get the repository migration right, especially the separation between mutable repo and immutable repo. AEM 6.4's new repo layout is definetely something you need to follow strictly to get it (and maybe that's not even enough, noone knows at this point).
Typically the public announcements about the 10 biggest new features for the upcoming release are made during Summit, and I would expect that if a CompositeNodeStore would be fully supported, it will be announced there (maybe under the slogan "Docker support").
I guess that we all have to wait until Summit to get that information.