That's a thorny question: Do comments need to be in the base standard, or can that be offloaded to those building on it? It doesn't look like it would be hard to have (comment "foo bar baz") in an expression and have a re-parser throw that out.

Is the complaint that no two groups of people will use the same comment standard if left to their own devices? It's not like the other data from different sources will always match up. What's one extra, and fairly easy to handle SNAFU?

That said, yes, I think I'd be more comfortable knowing there was an accepted comment format. The aesthetic seems to be Lisp-like, and I notice that the Lisp comment marker, the semicolon, is currently a reserved character, that is, it's illegal to use it unquoted. Maybe they're thinking of adding that at some point.