Well, technically, any board can be an Espruino board with the right firmware :)
As for an official Espruino board -- Gordon can answer that, but personally, I'd keep the focus on STM32 and NRF52. RP2040 has some very interesting capabilities, but for me, Espruino isn't about having the most powerful/versatile/etc. board around -- it's about a very short idea-to-implementation distance.
The major thing that sticks out for me is that RP2040 does not have very low power modes -- the current crop of official Espruino boards (and even ESP32/ESP8266) can go down to microamps in sleep, while the published numbers for RP2040 say the least it can go down to is about a milliamp.
In any case, I'm going to give porting Espruino a shot, as soon as I get the hardware.