Just a thought, I haven't even tried it yet, but what happen if you have a crusade against a Horde? Does the kingdom created revert back to Nomads when the king died? Can you create dinamic duchy "kingdoms" like you can in the Middle East?
I actually tried it this morning. The benefactor turn all the counties without holding into tribes. So tribal kingdom. And it doesn't revert back to nomad when the person die. Didn't expect that.
That's normal behaviour for non-Nomads taking Nomad counties, though.
Not the last part - when conquering a nomad province, it turns tribal. If it´s not upgraded when the conquerer dies, it reverts back to a horde.
So it basically creates a newly founded tribal kingdom? Interesting.