I see in the notes of the library that there is planned support for

I see in the notes of the library that there is planned support for the STM32 MCU - Is there currently any progress being made on this or is it a long term plan?

There is support for the Spark Core presently. That’s the only STM32 variant that’s actively developed and tested against/supported.

Is Spark Core an ARM Cortex M3? I really would love to have a port for Cortex M4 (Espruino Tiny for example)

It actually doesn’t matter whether it is m3 or m4 for porting, because the problem with porting is the low level pin and peripheral accesses which change based on manufacturer. The m0 adds some extra irritations in porting.

In the interests of my own sanity I’m putting a moratorium on myself for new platform support/porting for a little bit once I finish the m0 work needed to finish teensy-lc, rfduino, and arduino zero support.