As if IoT manufacturers weren't already ignoring the security of their IoT devices and properly updating them.
I think if IoT devices are to adopt a good open source RTOS it should at least be one written in a memory safe language.
Did I miss another option?
And there are some options. You could achieve barebones VM protections with Pawn(the language enforces very little otherwise, though). You could use something ref-counted like a TCL implementation, which would allow you to design around linear allocation times. The vast majority are using some kind of tracing collector of course, but I wouldn't say this is a total loss for achieving a combination of real time and memory protection.
PAWN for instance is explicitly 32bit and interpreted, so would run dog slow on something like an Arduino.
Something refcounted like TCL implies tons of heap allocations, which implies fragmentation at the very small RAM sizes of a lot of these chips.