The problem is that your observation isn't true. Here are some of the under-the-hood changes in just the most recent releases of Android:
-OpenGL ES 3.0
-Bluetooth low energy/Bluetooth AVRCP
-restricted profiles
-VP8 encoder
-new DRM framework
-SELinux
-various other optimizations and APIs
Yes Google is moving some functionality to Play services. Yes it is worth discussing how this may impact the future of Android as an open platform. No, that does not mean that Android is no longer "meaningfully open", especially not in the matter-of-fact way you are presenting it.