For sporting clays I think 30" to 34" barrels are here to stay. I read somewhere not to long ago that Mr. Digweed has switched to 32" barrels. In the artical I read he stated 34" seem to start some sort of problems. He did not go into it.
As for hunting I would think it would really be dictated by your terrian and what you feel you shoot best. In the Northeast were I am from I duck hunt with 28" on my auto, and 30" on my double guns. Grouse and woodcock I use both a 28" and 30" barrel on depending on the gun I choose to take afield. When I am out west in open areas I really like the 30". However when I am in Southeast Alaska hunting I like the 28". Devils club and thick forest can be a pain to get thru with or without a gun. But once I am in the Muskage its pretty much open country. Duck hunting in SE Alaska I pretty much stick to my Auto. Its always wet and alot of times in and out of boats. But I have hunted the Juneau wetlands and Montana Creek on nicer days with my doubles. I like 30" barrels for hunting.
Just my opinion. Based on what I seem to shoot best. As for trends I don't think in sporting clays it will ever go below the 30" in general. I do not shoot skeet so I don't know about that.
