> And I'll tell you what else. How about a nigh-on unhackable ROM-based, compact and lightning-fast but still fully-featured, and Open Source, OS to power the IoT?
It would, but the trouble with it being ROM based is how to patch a vulnerability that is undiscovered at the time of shipping - as we've just seen with Amazon's Free RTOS. To quote Douglas Adams "the problem with something that is designed never to go wrong is that it is a lot harder to fix when it does go wrong than something that was designed to go wrong in the first place".
Of course you could take a small RTOS and subject to it to much scrutiny, or take a mature RTOS on the grounds that any vulnerabilities would have been found by now. There's also active research in OS kernals that are mathematically proven to do what they're supposed to - Formal Verification.