An AR coating on the output face will allow a few more percent of light to exit, raising the efficiency. The sides of the optic will still internally reflect due to the angle that the light hits them. This is why the best prisms have AR coating on the input and output faces, but still function as prisms.With the optics its going to be artifacts and/or badly scattered beam pattern.
I do wonder why the major optics companies haven't gone AR yet. Though for "tight spot" type use, AR coating will mess that up, but something designed for wide pattern already it could be interesting.
Major optics companies, like Canon and Nikon, probably do use AR coating on prisms.