There's also MPU in even simpler/cheaper MCUs. For instance, ARM Cortex M0+ sports an MPU, and this architecture is used in STM32C0 ($0.24 in bulk) and RP2040.
I have no idea how the landscape looks in general, though.
The vast majority of modern MCUs have enough memory protection for Tock. Anything cortex-m0+ or "better" has an MPU. RISC-Vs PMP or ePMP as well. Most 16-bit "legacy" (though still popular) MCUs don't.
Virtually anything with a radio these days (the MSPs were holdouts but mostly those are Cortex-M these days as well)
Virtually anything with a radio these days (the MSPs were holdouts but mostly those are Cortex-M these days as well)