The primary focus of MIDI was for communication between synths and computers.
No, you should possibly read the article again. The first noteworthy MIDI connection was made between two keyboards.
But then, it's not even about that. Because, even if it was meant to connect a computer (which, back then, didn't make much sense as there was hardly any software to work with), the "nature of the data stream" is every bit keyboard centric. The main informations transmitted at first were note on/off and velocity, followed by certain controllers.
All of this is extremely keyboard centric as these are the very informations you can gather with ease from keyboards. Gathering the same information from a guitar is a fundamentally (!) different process, not even just because it involves pitch to MIDI conversion but because a whole amount of other information is much more difficult to gather or even needs to be stripped out entirely as to not confuse the receiving side of the system.
Sorry, but saying that MIDI isn't mainly suited to deal with keyboards is ignoring both history and practical aspects.
Guitar was and is still a challenge to confine within the limits of a 40 year standard that is MIDI. This we can agree. That doesn't mean it wasn't intended to be a part of the action from the beginning. Roland, the company along with Sequential that came up with MIDI, had guitar synths from the beginning.
That is just not true. MIDI has been developed completely without any guitars in the making, Roland was using a different data format for their guitar synths internally and only hopped onto the MIDI train when it became clear that this was the new standard. Internally, they continued to use something else (probably pretty similar but suited better for guitar).
Yes, Roland was involved in developing MIDI, yet, their guitar synths weren't part of the MIDI development.
It is to me a worthwhile historical discussion
Same here. And again sorry, but you seem to be sort of missing what the MIDI roots were.
Seriously, you can even see it by the nature of MIDI and the partially huge issues coming along with Guitar-to-MIDI that these two languages simply don't translate well into each other. Can you use it, though? Of course. And it's partially excellent. But saying anything that a guitar would be even remotely as suitable to control a synth via MIDI than a keyboard, well - IMO that's almost absurd.