They can already have the option of touching gloves when the ref bring them to the center before the fight begins if this gesture is really necessary to show mutual respect.
But after it begins, what's the point? Too many cases where one guy thought he was obligated to touch gloves and gets hit with a spinning back kick or worse. It's a dumb disadvantage to the one guy who thinks he's obligated to touch gloves. Happened with Rickson's opponent in a Pride event. And it interferes with long range techniques such as the long distance (i.e. Masvidal-Askren) flying knee.