I do understand why you want it to replace the Knight though, given the nobility connection. But to me, I think the Knight comes a bit late in the game for when the Huns histoically had their day. The timeframe doesn't seem to fit.
As I mentioned before, if it were me, I would have it replace the War Elephant with an increased Movement by 1.
A side effect of this, is it removes the slow War Elephant from the Hunnic arsenal. I would imagine an offensive machine that was heavily involved in mobile warfare, that was emigrated from a mountainous area (central steppes), would avoid using a slow animal. A second side effect is it gives the Huns an additional horse unit, again for a culture that "lived, ate and slept on horseback"
Also, having it replace the War Elephant will spread out the UU's a bit. Seems like a number of units replace the Knight (Arabia, Byzantium, Timurids), War Elephant has Khmer.
Hey Capo!
I think this is the best concept for the Hunnic UU. If i understand correctly, your main problem with this is if the huns do not get horses in the game, they would be doomed

But how about removing both the horse and the ivory requirement for this war elephant replacement UU?
I mean we are talking about the huns. I would like to see them having at least one type of mounted unit in every game. This way they would be able to build their UU even if they don't start neither near horse, nor ivory.
And of course, u could use Bakuel's units as Tarkan in the same way u wanted to, just replacing the elephants instead of knights...