Looking at the latest PicoCalc Picomite build it is 1.5Mb in size… The Pico2 flash is 4Mb.
This is just begging for some kind of dual/multi boot system with two or more images. Imagine having say Picomite, Python, C and MP3 player all selectable at switch on ?. The Pimoroni Pico plus 2 has 16Mb flash !! 
Hoping this stirs some creative results asap 
UPDATE - I’m not the first to think of this..
https://forums.raspberrypi.com/viewtopic.php?t=330960
And…
That link is for the Pi which has a bootloader and can run a real OS, unlike the Pico which is a microcontroller and runs firmware.
But I searched and found this link to an abandoned experiment from a few years ago:
https://forums.raspberrypi.com/viewtopic.php?t=330960
Not sure if that could be adapted into anything for the PicoCalc hardware, but it’s an interesting idea.
Maybe this could be adapted to load uf2 files from the sd card. From reading the code, it seems that the uf2 need to be relocated to make space for the bootloader in memory.