I have no unfair intentions with this.
Do not get me wrong, I have no doubt that your intentions are honorable. I am just pointing out that there may be a case of copyright slide here.

I will probably even tell other compiler manufacturers about the header file I'm creating and give it to them. It is my intention to help not just SDCC, but all 8051 C compilers (vendors).
I doubt very much a compiler vendor a will be interested in making his compiler compatible with compiler vendor b. I have no doubt that some look around the compiler market when the bill for the annual "maintenance agreement" comes in.

I was talking about helping derivative manufacturers to create one header file with (their) mcu-specific information for several tool chains. Atmel for example tried to do so, but did not yet get it right.
While the result of your 'help' would be beneficial, I doubt that many will be interested. Many '51 manufacturers are to a large degree 'linked'. For instance I think all Philips assembler code is for the '51 is in metalink format and most C I have seen is Keil formatted. I have been involved in several appnotes and whatever I have supplied (using 'my' toolset) has been taken 'as is' not "modified for wider acceptance". The Philips note with IAR code, I am sure, is another case of an "user supplied application note". The (sad) fact is that appnotes are directed to those that need them the least (professionals, not amateurs) and thus seems to be geared towards 'professional' tools.

I would suggest you contact Andy Ayre at esacademy (I believe he has no vested interest in any tool) who wrote the CodeArchitect which produce Keil C source to check for interest in your proposed 'universal' scheme.

One final note: what is the big deal? I have changed SFR definitiaons from one toolset to another in 15 minutes using CodeWright. Maybe some enchancements of your editor (column edit etc) would achieve the same.

I have 'inherited' several supposedly compiler independent pieces of code and always had to take the universality out to make the code readable (one instance removed 874 #ifdefs)

Erik