Unburden + Weakness Policy is a great strategy on anything that can run it. I've done it with an Unburden Hawlucha: Impish, 252 HP/Def & 4 SpD, running H. Jump Kick, Acro, Poison Jab, and X-Scizzor/U-turn, and even with Hawlucha's weak DEF stat, I've activated Weakness Policy taking an Avalanche, with slightly less than 1/3rd HP remaining.
Unburden Hitmonlee can probably do this more consistently than Hawlucha, albeit with slightly different type coverage, dude to it's high SpD, but Unburden Sceptile is just uncalled for. Adamant nature, 252 EVs in HP/Atk, 4 Def. After W.P./Unburden activates, Atk = 590, SpA = 442, Spe = 552, with no investment, fast enough to blow, well, damn near everything, in the dust. I'd run Leaf Storm(for PWNage)/Giga Drain(Recovery against Sucker Punch), Earthquake, Acrobatics, and Rock Slide, and that covers EVERYTHING, hitting 580/774 Pokemon out of the entire game for 2x or 4x damage.
Drifblim may be able to severely abuse Weakness Policy as well, once transfers to 6th open up, because it learns Recycle as a B/W2 Move Tutor move. From there, there are too many options to list. Drimblim's HP stat is ridiculously high enough that he can easily sponge a physical SE hit with max Def, access to Calm Mind to boost SpD and SpA on top of Weakness Policy boosts. And, if Weakness Policy boosts can be Baton Passed, he can do that too, as much as he wants, by use of Recycle.
Weakness Policy is easily the most interesting item this Gen, lots of potential.