"Rashere - For the Prophecy of Ro warhorse, I'm planning to allow you to turn in the claim item along with a normal bridle and receive a warhorse that moves at the speed of the horse summoned by that normal bridle. So, you can either use the base speed warhorse or get yourself a faster one through the turn in. "
-from the stratics dev chat last night
also briefly mentions that Knights may get some sort of deal to turn their mounts into warhorses (said it might not make it in this expansion though)