I like your platform, and I understand your position, but please, let's be realistic.
Adobe abandoned AIR for Linux (there will be no new AIR versions). Basically, what's done is done, some functions are not supported, and there is no room for performance improvements.
Linux is free, but hardware is not, hardware requirements for the same performance are already much higher on Linux.
You announced that your new Windows desktop player will fully support hardware acceleration, so cheap Intel Atom based, and similar AMD systems, should be enough. Further, because of low power consumption, it is easy to make such system with no moving parts (passive cooling and SSD). Any professional knows how big advantage this is.
If all of this happens (and you say it will), Windows system (with OS costs included) will be cheapest, and very reliable solution.
Regards