certainly there are people who have their own reasons for wanting to use an 8051 but want more than a 256-byte stack or to have more 16-bit registers.

We all know that typical school projects for the '51 is "the calculator", "the clock" and such. Those, I am sure, could benefit from stacks and registers allowing most code to be offloaded to an OS.
I have the very strong feeling that those that "have their own reasons for wanting to use an 8051" are not volume users. Non-volume is typically where buying tools to use a different (better choice) uC becomes cost prohibitive.

In any project I have participated in where the uC purchase was over 10.000 pieces a considerable amount of time has gone into choosing the uC, rather than discussing "how can we do this with THIS uC?"

The question is, will anyone that:
* use millions of chips
* have chosen the '51 over the ARM or other alternative
* refuse to use "proprietary tools"
need any of the above "improvements to the '51"?

Today when you can buy an ARM for $3, I doubt it.

I think that the '51, in order to thrive, need to push it's strengths, rather than try to be all things to all people.

Erik