Proprietary firmware is not a good thing, but it's not a very bad thing until we have open hardware, in my opinion.
a) Pragmatism dictates that in order to use the `new shiny' we use non-free firmware.
b) Ethical concerns dictate that no amount of `new shiny' is tempting enough to compromise our ideals.
I guess there are points in between and maybe these are poles in the debate with yer Stallman-types tending towards (b) and yer Torvalds-types tending towards (a).
I'd like a world without scary binary blobs and the Stallman in me chides me on my bad decision-making and lack of character. On the other hand, ooh look at the new shiny.
However, the question I care about is "does the original manufacturer have more power over the physical device I paid for than I do". If my Ivy Bridge GPU has on-board firmware, that I can't change, well, Intel probably can't change it either. Or if they can, they haven't documented it and so the kernel driver doesn't provide the facility and so effectively they can't, short of NSA-type hackery, an answer I am happy enough to truncate to "no".
However, for Skylake the answer to "Does the original developer have more power over the device I paid for than I do" is "very obviously yes" and no amount of handwaving or approximation will suffice.
Here, we're talking about a new micro-architecture for Intel's premium product line; I would be very surprised to hear Intel licensed anything in the design from third-parties. If Intel wanted their tool-chain to be available, they could make it so.
You can get a product out the door much faster if it use a off the shelf microcontroller and a EEPROM than a custom IC.
The GuC itself is basically a pentium processor running a very simple OS.