Someone was trying to make enemies be mounted, but it ran into major, major technical issues. Given that the guy who was working on mounted combat from release had only just started to get the mod kinda close to release when 1.6 hit (man do I feel bad for that guy), I'd say we have a fairer bet of Bethesda putting the final touches in before any users do on this one.
Ok, THAT guy is here, and still modding mounted combat in the shadow

To be honest, I already found a way to make NPC do mounted combat. This will be completely new AI implementation using true Object Oriented Design, coped with traditional AI Fuzzy Logic & FSM.
I will have to wait until DawnStar hits, to confirm that Bethesda would not do something like patch 1.6 again
