There's a discussion on ENWorld right now where some fans are basically saying, "We don't like the concept of X mechanic, and we're upset that Wizards even tried it, even though they discarded it." I think that's just senseless, and if you're one of those folks then I'm sorry but I think you're wrong. There is no reason not to try out a certain type of game mechanic if there is even a hint that it might benefit the game. Shutting yourself off to ideas, even ones that on the surface seem incompatible with what you're trying to accomplish, is both arrogant and closed-minded. The argument is "Clearly this is a bad mechanic for D&D, so Wizards is obviously screwing things up by even considering it" when it's certainly not clear by any definition of the word. There is no reason not to experiment with a certain type of mechanic, provided that you keep a clear vision of what you want the mechanic to do, what its repercussions will be on your game, and that you are willing to discard it if it proves to be a bad idea.
I think the real issue in that debate is that some people are letting themselves be blinded by specific mechanics instead of looking at larger issues. Basically, there are mechanical concepts and mechanical implementations. Mechanical concepts should absolutely be looked at across genres, I think. For example, one of the mechanical concepts popular in the Euro games that I like is that no one "dies" or "fails out" of the game, and everyone plays until the end. Look at Catan, Carcassone, etc. for examples. This is a concept that's already in D&D, though people might argue it's not. The key is not the concept, but the implementation. D&D currently implements this concept by making resurrection both possible and (in the grand scheme of things) relatively easy. Paranoia accomplishes it by giving you clones. D&D and other games ALSO accomplish it by allowing you to roll up a new character and join in.
I just don't think there's any reason to jump on the D&D designers for looking into alternative mechanics. I also think people are jumping to conclusions; just because someone says "We looked into an aggro mechanic" doesn't mean "we tried to use WoW's aggro mechanic." It just means "we looked into a method of encouraging a unit to attack a defender character" which is not the same thing. It's the whole mechanical concepts vs. mechanical implementation, and I think good game design comes from being open to the former (even if you ultimately reject it) and being able to create the latter in such a way that it fits your game.
