"wasn't predicated on this idea of quickly spinning up new, conceptual types with specific constraints like Ada/SPARK. That sort of thing is really either infused throughout a language, or it isn't used. It doesn't take a great deal of familiarity to see that much."

I agree that such techniques need to be infused throughout the language. I just don't know enough Rust to comment. I do love Ada's existential types. That's a very simple technique that can knock out all kinds of issues, esp numeric conversions, that other languages have to go out of their way to avoid. Quite a few things like that in the language.

" I suppose on that front (and while I'm pushing Ada anyway) I should also mention Ada has a built-in concurrency model, although I suspect you may already be aware of this."

There was a myth among some users of Rust that it was the first to have safe concurrency. I bust that here an elsewhere citing Hansen's Concurrent Pascal, Eiffel's SCOOP, and Ada's Ravenscar in that order. SCOOP is most exciting given pedigree (Meyer et al) and CompSci research into it. I've seen people formally verify (read: fix) it, livelock/deadlock-free proofs, and eliminate performance penalties. Wild stuff. Rust is latest with safe concurrency but not first. Some CompSci person really needs to do a detailed comparison of these as that might be insightful.

"Yeah, this is the biggest bugbear when it comes to Ada. For what it's worth, there has been some new life on that front and people are working on improving things. So far it's still very, very early days though."

The very, very early days on getting a OSS community around a language that's about three decades old. Whereas I've been fighting C's of a similar age, there was little resistance to Rust, and one spontaneously emerged around Julia. You see why I have little to no hope for Ada? The only place I see a ressurgence of it is business sector where professionals that Get Shit Done (TM) might use it for long-term, mission-critical apps. Aside from what we like, it also has advantage of being designed for readability, easy integrations, and future-proofing. It delivered all that for decades straight. Just say: "Look, you'll be stuck with this app for decades. You want it written in COBOL, Microsoft C++, or AdaCore Ada/SPARK?" Ok, let's be honest: Delphi Pascal was a contender and my recommendation given ease of learning for disposable IT staff. ;)

"If it is, and we are looking at running with a new, safe language, at a minimum we shouldn't be forced to take some serious steps back."

I feel you there. Good news is that the Rust team takes feedback so long as it's productive. They're quite active here on HN. You'd have to learn Rust more thoroughly so you could say exactly what Ada has and it lacks. Maybe suggest how they'd add that without breaking current code as the language is in stable mode. They might bring it up to parity there.

"Finally, I know nothing about how Rust handles concurrency, so that would be another great comparison to see."

http://blog.rust-lang.org/2015/04/10/Fearless-Concurrency.ht...

"The plan was for this to be a rather temporary account, but it seems to have stuck."

Good. Far as name, you can ditch it for one easier to quote or keep the gibberish. Four karma points aren't a big loss. ;)