I believe that might make the program rather large, though it seems like it should be easily implemented in a plugin--maybe the same one that will (hopefully exist) allow editing of the syntax file without (assuming XML syntax file format) XML knowledge.
Are there still people actually contemplating XML-format for syntax files?
How editable the syntax files should be is actually a quite hard question. No doubt will there be people who add bad keywords into their files, making their syntax definitions wrong. A definition for HTML, for example, might have "FONT" and other keywords no longer part of it added, making the users write bad and faulty code. On the other hand, a syntax definition should be fairly easy to write and edit to ensure that a large library of syntaxes is established, as well as making sure that people can write syntaxes to suit their own needs.
Still, EE is not meant to be the perfect user-friendly program, it's meant to be powerful and versatile.