How about soldering microSD card directly to PCB?
I have soldered wires direct to an SD card before now (I needed an SD card connected in an emergency and had no suitable socket for it).  It worked fine, but I certainly wouldn't choose it, or anything like it, for production.

Firstly neither the contacts, nor the housing, are designed for soldering.  Yes, you can solder them, but the plastic has a low temperature melting point.  That means no reflow soldering; no wave soldering; no clumsy drunken hand soldering.

Secondly, as noted in the comments, the contacts are not flush, so they would have to be soldered to something first before the whole assembly being soldered to the board (or something being soldered to the board first, etc).  That is extra cost, and extra time. I am not aware of any off-the-shelf part for doing it, so you'd have to pay for the manufacturing of it, pay for it to be installed, and pay for it breaking afterwards.

You're better off using a proper SD card socket. It has the advantage that the SD card can be changed when its write cycle lifetime has expired.