IF the controller behaves, and port multipliers are kept out, it might be usable.
But do we want for people to actually use it, come for help… and then we have to dive into details, how every single port is wired and keep track of which drive is connected to what? If not dragons, there are at least major headaches ahead.
Two JMB585 and a switch for 10 ports on a M.2 stick? Not without special dense and tiny connectors; as pictured above, two SFF-8087 get us to 8 on a M.2 2280, with no room two more ports. On a PCIe card? Yes, there’s space… but then a regular LSI HBA would provide 8 ports, extendable at will with a $30 expander. (These can work with a 4-pin Molex for power, no need to plug them in a slot.)
At worse, if the motherboard has too few PCIe slots available and too many M.2, there are these: