It ultimately depends on your definition of “serious” and the microcontrollers we’re talking about.

For performance-sensitive areas where deterministic latency is critical, a GC simply won’t cut it, even if you can control when to run the GC step.

For lower end microcontrollers, I highly doubt any of those solutions would ever work: there is simply too much “magic” (read: overhead) involved.

This is primarily why C is still king of the microcontroller world.