> Standard programming in C or C++

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.

What language do you suggest? The GCed languages aren't real time (yes there are hard real time GCs, but they come at the cost of overall perf and close to an order of magnitude more memory usage which is a non starter for many embedded boards). Rust support for AVR isn't mainlined and is frequently broken. It's Xtensa (ie. esp8266) support is basically non-existent.

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.