I'm not realy in favour for any kind of highlighting.
a) It distracts from the real content. I don't know anyone who would prefer a novel where punktuation marks are highlighed. I's maybe helpful for beginners - much like letter shapes on the wall for first graders learning to spell.
b) It gets less useful with languages that relay on libraries (like C) or macros (like Asm) as these can only be highlighted with knowledge about the libraries. Just highlighting the standard parts doesn't make much sense.
c) thinking of assembler, what good would be a highlighting iff all in column 8 to 15 gets attributed?
d) Or BASIC. Correct highlighting for all the MS-dialects will be a gigantic task - not to mention more interesting BASIC variations out there.
e) It gets totaly useless other languages that so not following a simple graph.
f) lets over all of this not forget, that RC is not about pages of inserted source listings. I do not expect (or want at all) see this.
To me a) already would qualfy to cancel this.
Last but not least, lets think about the meaning of this site - answering questions - so in an answer automated highlighting of some standard features of a language won't do any good, as this is (usually) not the point an answer is about. So the answerer needs to put up his own markers anway to point out the important pats - which in turn will fade against all the other blinkenlights, making it harder to understand what the answer is about.