I just realized that with this flower thing they discovered, at the end of the episode they can pretty much combine any two people and then separate them at will, with no danger. Starfleet can take their top specialists and combine them. Plus Maybe some freaky couples would sign up for it.
Yes I am convinced there are labs full of transporter experiments. Section 31 probably has its own lab but there would be plenty of rogue scientists. Someone is probably trying to make Klingon/targ hybrids to send into battle.