> I actually went looking for Rust development mailing lists, but found no discussion.
Here's a time [1] when someone mentioned rustup in context with TLS (it's release notes for 0.1.9). It's not that there's no forum to discuss these things.
If the discussion is missing, it's likely because it hasn't mattered enough for anyone to bring up yet. Rust is much more bazaar than cathedral. A GH issue like "my company's MITM proxy breaks rustup" doesn't mean that the Rust dev team drops what they're doing and rallys to solve this problem. Even if it comes with a PR, it doesn't mean that Rust should be forced to either accept the PR or shift resources to make the PR satisfactory.
> It's not fine to use security as the big hammer that cannot be argued with
People place an enormous amount of trust in their compiler and the tools ecosystem that surrounds it. It's extremely wise to be hesitant to permit an opt-out for a security feature.
Here's the real crux of the matter: if one wants a feature in your favorite open source project, they kinda have to be willing to hustle a bit. Nag some design owners about what is unsatisfactory about your proposed approach and what other design options might work instead. For all of the examples that you might find in other languages' ecosystems that already support this kind of a feature, you should be thankful that someone before you came across the problem and doggedly pursued a solution. But it's not a systemic problem that Rust doesn't have a solution yet: just another feature-in-development in the queue.
> and then – nothing happens
This is remarkably common among open source projects. Code contributions wither on the vine because it can sometimes be a lot more work than someone's interested in to push it upstream. IMO Rust is actually better than the average open source project in this regard (meaning fewer orphaned patches).
[1] https://internals.rust-lang.org/t/beta-testing-rustup-rs/331...