Technically yes, you were right, there is a chance for us to intercept the communication between PCH and the Intel CPU then reverse engineer the protocol or eve

Technically yes, you were right, there is a chance for us to intercept the communication between PCH and the Intel CPU then reverse engineer the protocol or even directly RE the PCH chip and create a substitute. But how practical, I don't really know. Firstly, the effort required is beyond most people can afford IMO. Put those cost/effort etc. aside, there might some undocumented CPU features actually need ME to work and if I were the designer, I would at least use signed if not encrypted payload, then make the RE process much less likely. Regarding why I was thinking the government(s) involve in it, actually it quite natural. At the very beginning, I would say it might be for IT management purpose only, and soon someone just like you mentioned DRM etc. get added to it. And I don't see a reason why government(s) don't see the value of it and would not want to get in as there is nothing better for large scale surveillance: built-in with almost every single machine, have access to virtually everything on the machine, powerful enough to do what ever they might want to do and most importantly, most people have no idea about it and even if someone like us happen to know it but nonetheless, we still almost absolutely have no way to remove it or at least disable it.