The SM-6 is primarily an anti-aircraft missile, a modified Coyote could be used as either an AShM or an ARM also by fitting it with a Mk-72 booster it could be fired from a ship's Mk-41 VLS instead having to launch it from a land based facility.
Yes, I'm very familiar with this weapon
The thing is, SM-6 seems to fill the need for a high-speed AShM nicely, with significant range and nasty terminal effects thanks to its near vertical arrival at high speed. Granted, it's not a sea skimmer, but not many ships are set up to deal with a volley of Mach 4+ high divers either.
For sea-skimming, there is a pretty strong school of thought that faster is not always better. It forces you higher and raises your IR signature, both of which increase detection ranges. Low, slow, and preferably stealthy, is very effective.
I think a pairing of SM-6 with Tomahawk MST, NSM, or (ideally) LRASM is a very potent combo that stresses the hell out of a defender. Coyote doesn't add significantly to their problem set, especially given the tiny (barely OTH) range it offers.