Espruino Pico Adaptor PCBs

Are you planning these for the 0.05" header only, or both? I think for the 0.1" header, many of those things wouldn't need it (like CC3k, RFM, Wiznet, ESP, etc) - just a couple dupont jumpers and you're good.
Then again, I think those'd be perfect things to put onto those 0.05" headers, so connecty boards for that would make great sense.

I really like the idea of being able to stick an LCD right on the board - that's also the sort of thing that makes a long more sense on the pico due to the lower price point and smaller footprint.

I'd say:
AT24 I2C EEPROM, or AT25 SPI EEPROM - I think one or the other would be helpful? I've put EEPROMs onto the prototyping area on 2 of my 3 Espruinos - there are just so many times working with a microcontroller when you want to store just a few bytes in non-volatile memory.
ULN2003/2803 board (put the pads for a 2803, if we want to use a 2003, it could be installed, just not using the last pair of pads), giving us 7/8 higher current outputs on 0.1" header
SOT-23 MOSFET board - as with the ULN2003/2803, only with a buncha mosfets, with pads for a resistor between gnd and each gate for a pulldown.

Is the list of what pins will be on the 0.5" header finalized? This would have some impact on what things might make sense.

What's the footprint of the shield/adapter/coaster* board going to look like? Will it only have one set of 0.05" pin header, or will there be a second set (maybe on the opposite end, rotated 180 degrees) to stack them?

Have you tested that the 0.05" pins form a rigid enough connection? Will we need a little rubber bumper or something under the board to keep it from getting damaged wiggling around?

*"Coaster"? Arduino has "shields" - what would you put your cup of hot javascript on, if not a coaster?