1) Rust's use of LLVM means it will not work on some hardware platforms that the OpenBSD folks are committed to run on.
2) The Rust project currently does not offer a long term support release.
These are important to the OpenBSD team. Additionally, I am sure that they value the memory safety that Rust offers.
I wonder if the OpenBSD team would ever design a systems language?
If it works out there, OpenBSD could audit and import things at their leisure, at least in theory.
Here's an example from one of the leading groups in the field:
http://www.cs.cornell.edu/jif/
That was turned into SIF, Swift, Fabric, and I think Civitas voting system. Swift even auto-partitions the system between client and server side while maintaining confidentiality/integrity policies. Fabric kicks butt on all kinds of issues in the hardest space of them all. So, given the above, I'm sure a problem like Heartbleed in a mere SSL protocol would be trivial to prevent at language level if software and compiler developers merely chose to adopt info-flow security at least for important projects.
Note: One can use stuff like that even if not supported in main tool set by creating a mock-up of software in supporting toolset. The abstraction gap presents issues but a problem in one might mean problem in other. Especially for what amounts to covert channel analysis of software.
1. Object X frequently removes limbs from the user.
2. Object Y does the same thing, but more safely.
3. Wait, Object Y causes hangnails if you misuse it hard enough.
4. It's OK to keep using Object X!
Like many fallacies, this doesn't survive being clearly written out, but I still see it an awful lot.
The OpenBSD folks have done great work through auditing and writing safer code in C, and I agree that using a language that ameliorated at least some of the common mistakes programmers make would be a net positive.
Related - this blog from @tedunangst is worth reading, regarding the limit to which even a language like Rust can protect against specific exploits (the OpenSSL "Heartbleed" vulnerability, in this case) http://www.tedunangst.com/flak/post/heartbleed-in-rust