Thank you for detailed input.
Yes, the memory issue has been seriously considered in the design. You could see in the first picture there is an on-board SPI-FLASH. And there is a TF card holder as well, enables to add extend tf card for more memory.
Actually, even on the latest released basic expansion board for Seeeduino XIAO, there is a bonding pad reserved for extend SPI-FLASH. May have a look at:
May I ask how big will be your prefered memory space for an onboard SPI-FLASH?
Welcome to share more thought on this.