They can prioritize all they want, but no one wants to pay for the carrier certification of thee modified SDRs, particularly when using a T-Zone on a Snapdragon chip in order to run the baseband, and the FCC demands that the SDR be certified as a unit (software + hardware). That's a carrier certifiiation per carrier, per country, per device, per version update.
Heh. That isn't the problem. Unfortunately, I can't explain in more detail, because my conversations with carriers are confidential.
Also no carrier using a contract lock-in revenue model is going to provide an update that doesn't lock you into a new contract
Also not the problem, and I also can't explain. I'll just point out that the carriers have so successfully branded Android as their own that many consumers see the failure to upgrade as the carriers' fault. The carriers aren't blind to this, or what it costs them.
You should also be aware that the image that's shipped by the OEM is often not even buildable by Google engineers
Why yes, Terry, as a Google Android engineer I'm quite aware of this :-)
Except you should replace "often" with "never". Or at least "almost never". There may be some exceptions, though I've never heard of one.
apart from the fact that the devices used during development are generally signature neutered
A bigger issue is that the devices used during development are Nexus devices, not OEM devices. We never see those, either the hardware details, or the code that OEMs build after all of their customization.
Seriously, one of the smartest things that Apple did was keep the baseband processor separate from the application processor so that there was no telecom recertification required, unless they were explicitly hacking the baseband for some reason
That does make a lot of sense, but I don't think it's actually relevant to the problem. The carriers validate a lot more than just telecom functionality on devices that carry their brand.