They don't confirm anything, people thought Light was going to appear in Gen V due to Reshiram's angel like appearance but it didn't, with Reshiram being Dragon/Fire.
Anyways I've had this thought for awhile, what if Xerneas is Steel/Electric with the horns being lit up by it's internal electricity? Lighting can sometimes look branched out too like horns. While the horns don't look electrical per say it is a possibility. Or maybe it's Grass/Electric...that'll be unique ;3