Espruino Mimetism

I just did the footprint ( SMD version ) of the Pico - would you tell me it it's precise enough ?

It looks ok, but honestly I have no idea how I'd check. Best bet would be to print it out to scale, place an unpinned Pico over it, and check it looks fine.

About the "visual pin feedback", yes, it'd indeed be done via a Serial msg callback to the laptop

Honestly, this would be a nightmare to do - if you sent back a message every time the pin changed state, the state changes would be so slow that the Pico would be effectively useless.

In simulation it'd be fine, but in real life I don't think it's useful. If you want the functionality it's better to just spend £50 on a logic analyser :)

even if the bootloader doesn't

I mean that while you can update the Pico's firmware - you can't easily update the bootloader (so its harder to brick the Pico :). That means that you will likely not be able to use the 10.6.8 to update the Pico's firmware, but once it is updated on another PC, you can use it fine.