So this is pretty much about breaking the client side DRM, with a bad side effect of abusing someone else's Identity (as used within the DRM context) for nefarious purposes. Did I understand this correctly?
The attack essentially means that they could write a program themselves that acts as "Windows.Media.Protection.PlayReady.dll" to get decryption keys from a server. What will happen now is that Microsoft will deprecate the client and release a new one with new obfuscation and new keys. The license servers will start rejecting the old cracked client. And then people will crack the new client. And the cycle continues.
Thanks for the clarification.
Otherwise people would be worried about being targeted and having "personal" keys tied to a financial account or online identity getting sold and used by others to access arbitary content.
This seems kinda good news for concerned users, but even worse news for Microsoft.
The decryption keys have to be stored on your device so you can play your media or your game. So, the level of encryption is totally moot. The level of obfuscation is all that really protects the content.
Basically the means to forge an authenticated cookie.
[Update]
It's a bit more subtle: Having the keys to forge a license request and decrypt server response allows you to emmulate or re-implement a DRM client.
Because the server is oblivious to this fake, it will respond as though it's taking to a genuine "secure" client thereby ultimately exposing the content decryption key.