/dismount
/castrandom [flyable] Swift Purple Windrider; Reins of the Tan War Talbuk, Reins of the Silver War Talbuk, Reins of the White War Talbuk, Purple Skeletal Warhorse, Whistle of the Black War Raptor, Summon Dreadsteed(Summon)
This is the macro I have been using, it's worked the way I expect it to. As you can see it can also randomly choose my warlock mount, so that code does indeed work.