"My understanding is that Rust doesn't have so much to offer Ada/SPARK. I haven't looked that hard at Rust though, so maybe I've overlooked some of it's features."

I liked the juxtaposition of that haha. It kind of negates anything about Rust in your counterpoint. Your points on Ada/SPARK are still worthwhile.

"Ada offers..."

No doubt. It was systematically designed to reduce the existence or impact of flaws throughout software. They kept this up in extensions. SPARK straight up proves the absence of them in a subset. So, it's what my gold standard is for safe, systems programming. Rust is the newcomer with interesting additions inspired by safer-than-C imperative and functional languages. It's confusing scheme for memory and concurrency protection is said to be quite effective. It might end up better than Ada over time or just different tradeoffs. The important thing, though, is that it has what Ada/SPARK will likely never have: large-scale adoption with uptake by big companies and users who will add to its ecosystem. Ada FOSS community is barely there with biggest deliverables coming from AdaCore.

Remember Gabriel's Worse is Better? Real lesson of it is certain things get adoption better than others. Best to bet on them. Rust is in that category a bit but with Right Thing elements. So, it's worth investing in for long-term benefit of IT.

"I'm also not sure why you would want to abandon the actually verified properties of Ironsides for a hope those properties remained in an unverified port."

I'm not necessarily suggesting that. There's a reason that OpenBSD and some proprietary vendors keep their system working on several compilers. There's a reason NASA project here used 4 static analysis tools. There's a reason B3/A1 systems kept detailed, formal specs side-by-side with code with both checked. The reason is that different tools catch different types of problems. Further, a problem detected in one might apply to the other. Now, a semantic difference exists between Ada/SPARK and Rust. Yet, there's usually a subset and/or style one can use where results from one about memory or control issues will apply to the other.

So, I said do it in parallel: both Ada/SPARK mix and Rust. It displays how each language handles the problem. It let's the analysis tools of each check it for problems that might exist in both. Tool version of many eyeballs except works consistently. ;) It also means that compiler optimization problems in one might not affect an other. Can help with hotfixes while compiler team develops guidance or patches. Also, provides two implementations that can help with adoption and support. There's an issue of maintaining parity but the simpler version is write it in Ada/SPARK w/ Rust release getting uptake.

That's the lines I was thinking on. Rust is popular and better than usual. Ada is equal or better in capabilities but not going anywhere. Leverage both to get benefits of both maybe defaulting on Rust release for adoption. Far as Ada vs Rust, I'd like a less biased party that knows Rust's protections and features through and through to do a comparison for me. I have a reference listing each issue Ada tackles and how. I probably can dig up one for SPARK 2014, too. I would love to see what mainstream answer to Ada can do vs the baseline it created.

Note: You should get a real account if you're a programmer AND know Ada/SPARK. Seriously under-represented here.