As I have mentioned before, one potential issue with the overall security-robustness of using SpecC (or any other HDL which makes use of testbenching) is that several "trampolines", written in native code, will be needed. The trampolines won't be very large, of course, and it should be possible to test out nearly all of the potential bugs - in any given code release, of course, and then there are the issues of supporting lots of different hardware platforms, with a concomitant increase in total code size.
One of the ways around this may be to write the native code in a different language than straight C (and possibly even assembly language as well). I have been reading up on the Rust systems language, which is designed around code-safety, and specifically the elimination of pointer-related bugs. The Rust authors claim that it fixes most of the security and reliability minefield that straight C is known for being. I don't plan on making a serious attempt as learning most of Rust, let alone integrating it into Controlix, for a while though - at least until Controlix's first beta release. Too much other stuff to deal with... definitely something to keep an eye on, though.