Trademark law is not that dystopian, it concerns naming products, not everyday speech. Writing (and reading) a trademark use policy with those boundaries in mind seems non-controversial to me.
The most basic rule is that the Rust trademarks cannot be used in ways that appear (to a casual observer) official, affiliated, or endorsed by the Rust Project or Rust Foundation, unless you have written permission from the Rust Foundation.They're saying things like "may not do that" and "cannot be used unless ...", when what they really mean is "we're not granting any special permission to do that", and "cannot be used unless ..., in cases where your local trademark law says you need our permission".
Creating a fork to contribute a PR is not an issue. If you fork and diverge while still calling it "Rust" then you're probably in hot water. Even then, no one would care unless you amassed a following or notoriety for it, most likely.
Used in what context, though? As far as I am aware, each trademark is only granted for a specific list of market segments. Anything beyond that, and beyond offering products/services, should be (mostly) in the clear.
I think it's a good idea from the Rust Foundation to prevent others from naming threir convention "RustCamp" or something similar, and I don't think they're doing much more.