I expect UFS memory cards or relativey high grade ones to act as cheap and versatile SSD, that will make them more affordable and interesting : use as a system drive in a desktop tower, then as USB drive or in a mobile computer.
Till then, using a smaller old hard drive for the OS has worked for me : similar space, I/O benefits from having the I/O come from different drives. Other small benefits.
For rusting desktops, there's lack of SSD or memory cards slots, lack of controllers. 1x PCIe card that takes cards would be best and it works with new or recent PC, or even in a mini PCIe 1x slot.