Yeah, the more I think about it, the more it makes sense. I would assume based on the arguments made in this thread that a large portion of the Onyxia population that is worried about blackrock item progression, are probably not die-hard arena fanatics. They're of course entitled to their opinions, but it's safe to say if you are citing Gorehowl as an item that you're afraid of Blackrock players purchasing, your experience in TBC arena is on the newer side.
Not saying this as a jab, I'm saying this as evidence that these players are probably going to be duking it out in the 1500-2000 bracket. If we gate the trinkets to 2100+ or higher, then the people who are afraid of this item progression will not see blackrock players with these items since those blackrock players will be too high MMR.
The blackrock players that these Onyxia players would be fighting would in turn not have these trinkets. Blackrock players still get to purchase and play with them, and have something to strive for. And Onyxia players don't have to worry about the trinkets.
Seems good on both ends.
(I again want to cite that these trinkets don't make as much of a difference as they are claimed to make regardless, but I digress)