OK, the word stupid is a bit harsh. Apologies if I offended. They are mistakes I would have made in my early days too.
I am not really worried about U20 missing, but I was more interested in what purpose the designer had in mind, and why he/she chose that particular (chinese only?) device.
U13 is very low capacity, and replacement with another device would seem prudent (a true uSD for example). However, I wonder if U20 was meant to be a SRAM/FRAM device (not flash/EEPROM/etc) to increase the amount of RAM available from the minimal amount in the CPU (and FPGA), and hence allow true RAM access without worrying about write cycle longevivity?
There are (few) applications where more RAM is required, and it would be nice to not worry about endurance.