Hypothetically, would you count a good implementation of an 8051 core, or reject it because it's an 8051? Likewise, would you reject a core that didn't implement some standard architecture, because of toolchain issues for assemble/compile/debug? What about architectures that are merely "really old" ?
This is a real, and difficult question. I know that I've looked at some popular commercial microcontrollers recently and thought "Eww. It's unpleasantly like a Z80 with a bunch of bells and whistles attached, and a single-source C compiler." Or even: "I loved the PDP10. But without the whole ecosystem that surrounded it, including the "significant user base", I'm not really inclined to want to spend much time programming one, any more."
And people are rejecting PIC32s because they only use the 2nd most popular (?) purchasable CPU IP...