at people who say G&W will fall...
But I will say that he is in the same position as DDD. Each character's metagame hasn't done anything in so long.. Well at least G&W has bucket braking. It is too good. I have gotten into the 200%'s against characters like Diddy by playing smart.
I really can't see Diddy hitting top 4. Yes he does well against most of the top tiers but just look at who is ahead of him on the current list (though outdated yes.. but that's what we have to go off of). MK, Snake, Falco, DDD, G&W, and Marth.
Definitely better than Marth, I would say G&W is debatable, and the other 4 I would say is currently out of the question.
In the long run maybe. I see G&W falling to like 6th or 7th just because he is such a solid character but won't have anything new. G&W players will eventually just have to be the better player once people find ways around him; I see 4th place staying with DDD or going to Wario before Diddy.