In addition to blending different beers (like, blending an stout with an IPA, getting something like a black IPA), it's important to mention that almost all barrel aged beers are blends, because of the very nature of barrel aging.
When I mention barrel aged beers, I'm not just referring to the recent barrel aged styles which have been created by the american craft beer scene, but also to more traditional ones like the Belgian ones: lambic, flanders red and oud bruin.
Blending is crucial to beverages aged on barrels (even whisky or wine), because you never get a regular result from them. It depends heavily on the barrel itself (remember, it's wood, a biological element), the storage conditions of each of them (temperature, for example, which varies depending on the position of it in the warehouse) and some other random factors. So, the only way to achieve a consistent and reproducible product is blending, trying to fuse all those different characteristics in the right proportion, giving you an expected final product. In this process, is even common having to dump some barrels, which will not make it on the final proportion (maybe, let's say, you have too many very sour barrels, and you don't want your beer to be so that sour).
Additionally, another common practice is to blend aged beer with the young (not aged) version of it. Beers like Rodenbach, for example, are like this (Rodenbach Grand Cru has 2/3 of aged beer with 1/3 of fresh beer). Dogfish's Burton Barton is a blend of wood-aged and fresh IPA, as well.
So, blending beer is not exactly a new thing. I understand that your question was about blending different styles of beers, which is still less common, probably because the brewers will try to do that from the beginning, with the ingredients, but is not an heresy. We should try doing this more often, I dare to say.