Can't find current player stats, etc.

Adobe Marketing used to fund a profoundly expensive program where we paid a third-party company to collect independently verifiable usage and penetration data on Flash Player.  As you can tell, we stopped doing that around 2011 as Adobe's marketing focus changed. Our general thinking is that metrics that we publish should be independently inspectable and verifiable, and we're not positioned to publish the source data from which we derive our internal metrics.  I did find a couple commercially available market reports for sale, but I can't speak to their accuracy or data collection methodologies.

My general recommendation when this topic comes up has been to encourage independent content providers to do their own measurements.  It's trivial to poll and collect data about Flash version and capability from your site's visitors.  I think you'll find that not much has changed since we stopped publishing official reports, but that may vary by audience.

I'm not aware of any requirements in China to keep old, vulnerable Flash Player versions around, and many of the large, massively popular online gaming sites in China aggressively take advantage of the latest graphics features.

We do provide various Stage3D profiles for the purpose of allowing you to target content to lower-end systems, but for specific features to be available, they all have to be running current version.  The vast majority of Flash users take advantage of automatic updates, although with every product, there's a small, long tail of users on random old versions.

Context3DProfile - Adobe ActionScript® 3 (AS3 ) API Reference