there are many interesting posts about ATS on Chris Double's blog

http://www.bluishcoder.co.nz/tags/ats/

I've looked at ATS a few times before, and I really like all of the ideas behind it (fast, ultra-powerful typing, functional) but the syntax still seems a little clunky.

In any case the ATS compiler can emit C code, so it should be easy enough to re-implement a few bits of code at a time instead of needing to port entire projects all at once.

Yes, it's possible to integrate ATS generated code into a C project. ATS provides control over the names of the generated functions so you can only convert the parts you want to be verified as safe by ATS if needed.

What does the question mark imply at end of the title?

People are always talking about how language 'X' is going to replace C as the next systems programming language. I think the question mark is meant to imply "Is ATS the next systems programming language?"