something like %package bla ... ... %files bla ... ... %description %files i.e. when main package information is following, doesn't seem to work. Yet it's a very nice thing to have (if subpackage info is %included)
What's really needed is the ability to include a "chunk" (i.e. another specfile) for a sub-package and have the Right Thing Happen, i.e. scriptlets merged etc. The scoping issues with the spec file parser you point out are examples of the problems that need to be solved. Gonna be a PITA, can't be helped. Changing component.
Does this look to be a possible rpm for the RPM-4.1/2 stage or something for a much furhter release?
Yes, this is doable, but is still low priority.
Spec file syntax cannot be changed, de facto is all there is.