I... don't like that this is required now and I kinda feel like it's an accident

I didn't mean to come off very opinionated with "blessing in disguise", I'm fine either way.

do you think it should be required? I feel like tightly-packed kdl like this should be legal, if only for practical purposes of data transfer: foo{bar;baz{quux a b c}}

That seems fine to me. One thing I wonder about is the interaction with slashdash comments:

• If foo{bar} is legal I would expect foo/-{bar} to be as well.
• If foo/-{bar} is legal I would expect foo/-bar to be as well.

So, (node-space+ slashdash? node-prop-or-arg)* should maybe be (node-space* (node-space | slashdash) node-prop-or-arg)* or something equivalent.

no worries. I think this is a minor thing that we can justify slapping on as a patch.

I'm seeing the RFC process as another opportunity to iron out things we've been discovering since the initial 2.0.0 release, too. THAT is gonna have to be seriously solid, but it's going to be a long process.

and yes, I like your suggested edit to the grammar. I think we should do it, tbh. I'd love to hear from others, though.

No real opinion, fwiw. As long as it's unambiguous I'm fine with compact parsing.

Let's get a PR, then? :)