I did that with PalmOS - a card that you insert into the original Pilot (16MHz 68k) and it takes over, runs PalmOS5 on a 200MHz ARM chip, using the pilot as a display and touch panel. Also did it using memory stick IO protocol too (Ctrl+F for "MSIO")
As someone who got in to the PalmOS world just before OS 5 was shown off and then spent years waiting to upgrade for the OS 6 device that never came I've been fascinated by your project since I first came across it. Amazing work!
Amusingly the device that replaced my classic Palm was an Axim X3, which if I hadn't sold it to buy a server in 2005 would probably have already had your rePalm build installed on it.
https://dmitry.gr/?r=05.Projects&proj=27.%20rePalm