Compiling to C: yes, I've had that thought too. It's certainly attractive as a means of writing an initial implementation of an experimental language or one you aren't sure will see wide uptake yet, because as you say, you can get all the portability of C (up to OS API integration) and its performance too by using existing compilers. I think where it falls down worst is debugging – it'd be almost impossible to take a language compiled like that and get sensible integration with gdb or your other debugger of choice, and sooner or later that will become a serious pain. So sooner or later you'll want your language to have an end-to-end compiling and debugging story.

provided you remember to add the "don't leak this" boilerplate

Argh, yes, dammit, any time you find that you always have to remember to add the "work properly" option it's a sign that someone has cocked something up. My usual example of that is find -print0 or grep -Z piped into xargs -0.