In the Star Trek: Voyager episode Drone, the doctor’s mobile emitter and Seven of Nine's nano probes come together to make an advanced Borg drone.
Seven of Nine's dialog:
SEVEN: This technology resembles a Borg maturation chamber, but many of the components are unfamiliar.
CREWMAN: Commander. (They have found Mulchaey. He is still alive.)
SEVEN: He was punctured by an extraction tubule. It removed a tissue sample. There are residual nanoprobes surrounding the wound. Their encoding sequences are identical to my own.
Given that they have or can create a maturation chamber, why can't the Borg take alien DNA and harvest their own Borg, rather than assimilate?
Other than not hearing the "We are the Borg" introduction, what would be the problem?