Ed, I like your post. But I have to disagree a bit.
There's a group C/D/E/Etc.
There are a lot of user scenarios out there. I won't bore you with mine. I support the broad strokes of what you said. It just isn't that On or Off.
Well, maybe there
is a group C. In fact, of course there is, but generally I've found that those groups are just wasting their time. If Microsoft (or insert AT&T or your favorite carrier here) decided that the 1520 was never going to recieve the "official" upgrade, then it's just not going to happen. No amount of "user-voicing" or complaining is going to change anything. Look at the 830 users and their missing Denim issue - it's a done deal. I guess it could be acceptable to have a group C for users to vent, but I wouldn't expect any of it to change anything. To me, it seems like a recipe for disappointment.
I tried to be a "group C" user once, with my gaming desktop's video card. It all started when Call of Duty Ghosts came out, and I realized after purchasing the game for $60, that my top of the line at one time, $600 video card (the GeForce GTX295) couldn't run it, as the game required DirectX 11 hardware. My card was DirectX 10 only. No amount of complaining, or venting to the game's developers ever allowed me to run that game on that card. Couldn't they just release a patch, where I could run the game in "DX10 mode" without all the DX11 features? Nope! I needed a hardware upgrade, and deep down inside I knew it.
Sure, the 1520 runs the Windows 10 mobile Insider Preview builds just fine. Most of us here have tried it, and I'm still running it myself. But I know some new features aren't going to supported. Microsoft came right out and said "New hardware will be required" for these new features (continuum/Windows Hello/etc) and I believe that was the writing on the wall. I knew right then never to expect the "official" Windows 10 upgrade on my 1520. Why would they? They're going to be pushing the new hardware. Nobody would buy the new 950/950XL if their existing 1520s and 930s can do the same things. Maybe after the new phones come out, and all the dust settles, and sales of the new phones slow down, only then will they maybe release an official update for the older phones. It wouldn't be the first time, but by then, I'll have moved on to new hardware myself.
But yeah, I suppose I'll agree that there's other groups, or types of users. (C, D, E, etc) But they're all grey areas. The ones that still have their WP7.8 phones that feel "burned", or the Windows RT users with their Surface 2s that keep complaining that they should get Windows 10 too. It must be a miserable life, all that posting and complaining that never goes anywhere.
Software will always be capable of persuading people to upgrade their hardware. But hardware, I've found, always has a limit of how far someone can upgrade their software.