Hey guys, first time poster, long time lurker.
Recently on my Horde Hunter, I finally got my reputation to Exalted with the Bilgewater Cartel and bought my Goblin Turbo-Trikes.
Just last night I switched from Horde to Alliance to join a friend's guild on another server, and to my surprise, the Goblin Trikes were still in my mounts tab, and could still mount them.
Names and such edited out, but you can see in the bottom right hand corner that it's a Human Hunter, as well as numerous Alliance Mounts in the mount tab.
[spoiler][/spoiler]
I don't know if this is intended or not as there's no equivalent mount conversion for the Alliance mounts, but if you're planning to faction change to Alliance, get your Goblin Trikes today.