Pony looks really interesting and I look forward to trying it out. I can't help but try to reason about how my work language would handle these problems. Go.

Highly concurrent: check.

Predictable latencies: I think that's a check, the go gc has had alot of engineering put into it to provide good pause times. There are some edge cases still.

Data safety: I think go is weakest here in terms of language design. Go does have go build -race which works pretty well for me, but I can see how some wouldn't consider it sufficient. It also wouldn't catch single threaded ownership problems, which can happen.

Easy way to interact with other languages: via CGO and buildmodes you can trivially call go from other languages. Some don't like that the runtime is still shipped and started, but the fact remains that you can cffi go functions from python very easily.

I'll have to check out pony this weekend. I've read up on it a bit but haven't compiled anything.