Difficulty? Well, I suppose it depends on how difficult it is to play in tune..
At the risk of turning this into a drum corps thread --
Phantom Regiment did an arrangement in '93, and they put a hornline-only recording on the DCI Christmas CD, "Ornaments In Brass". Sounds really good.
I haven't heard the tuba choir arrangement, though. But, I'd probably want to hear some other colors in the sound besides just tubas (and euphs, I'm assuming).