I think this RFC is a bit misguided.
I have had this on my plans for a long time but never found the time - I
would love if someone took on this initiative.
The package xml for this is already ready:
https://github.com/pear/pear-core/blob/master/package-Exception.xml - for
the most part.
It didn't help that PEAR had deps on PHP 4, so the only viable option was
to make PEAR_Exception depend on PHP 4 as well. That way PEAR could depend
on PEAR_Exception and not the other way around, thus on the new PEAR update
people would get PEAR_Exception.
If we move PEAR it self to have a min dep on PHP 5 (5.1.6 or 5.2 perhaps)
then PEAR_Exception can dep on PHP 5 as well and everyone is happy. No
Package authors can them self do releases (or QA) with a new dep on
PEAR_Exception instead of PEAR, but it won't be required to do a mass
updated on all packages.
I want to see this done but not in the confusing manner proposed.