Well, I think this wouldn't really fit as well. I agree with Kabcsi on the traits. On the other hand people in the western usually think Huns were barbarians. This isn't true either, it's more roman propaganda then reality. Sure, they often were in war, but you can say the same about the Romans. So what I want to say is: please don't use phrases like "WTF" when we talk about this, okay?
Your idea for the UB is interesting, but I am not sure if religion was that important for the Huns. All I have read about the Huns that had something to do with religion, was that Attila was maybe a christian king (believe it or not). I also don't find priests that important in civ4, maybe I have a different style of playing it than you? Where did you get this idea for the UB? Can you serve with a source?
I also thought that mystisicm isn't a good start technology, but your suggestions seem to be very strong (especially mining). On the other hand I can't see how the Huns get their food if not by hunting. Huns were nomads, even when they settled down in europe, they haven't started agriculture or fishing AFAIK. The only way to get food would be raids, but that isn't enough for an empire. So what I want to tell you, is giving them hunting as starting tech. I also don't see what Huns have to do with wheels, but this may be due to may leck of knowledge.
According to the sources I have read, Huns didn't really used other units than horsebased ones. If this is true (well, that isn't necessarily the case, because I made the experience that german sources about Huns are poor; however, I can't serve with a source unless you speak / can read german...), then the UU has to be a horse based one. On the other hand, Huns had a great empire. They needed fast troops and they have simply overrun the Balkan. For these things nothing else then mounted units were needed.
When I play civ4 (always with Hungary), I used to research horsearchers early. That's not a problem. Other civilizations get their UU much later. But you may be right when you say the UU is weak at the moment.
well. i know about hunnish history very well and agree with you about your issue on the term barbarians.
huns have turkic root and believe in shamanism in that ancient era like most Turks before Islam.
+1 free priest every city is good. this means 1gold, 1 hammer and 3 beakers (with repr) for each city. why i thought of such a UB was for compensating the traits of Attila. i think everyone agree that Attila should have at least 1 warring trait, so as to suit his military skills good. so a UB helping economy could be fine.
if he would have 1 warring trait, then CHA is better than agg. especially if his UU would be a mounted one, CHA is much better if you would give him AGG/CHA, this is a good combo but it is hard about economy in high levels.
if you insist on a mounted UU, then chariot replacements would be better. sth like immortals maybe. a chariot with a free cover promot and a little less cost for ex. what about this?
or a scout replacement with free medic 1 promot? what do you say? it would be strange and useful with CHA, right?
it is your civ but i believe CRE/CHA would be very good for him.