Here's a detailed analysis of the effects that the E. Pluribus Hugo proposal would have had on the 2014 and 2015 Hugos.
Unfortunately quite disappointing to me. The 2015 Hugos would still have been Puppy-dominated (though there would have been some very salutary effects in terms of removing one or two Puppy-backed items in most categories; I especially like that an Ursula Vernon story and an Aliette de Bodard story would've ended up on the ballot), and the 2014 Hugos (which had no known prominent slates) would have lost several nominees. (For example, Sheila Williams would not have been a nominee if EPH had been in effect; nor would Galen Dara or Fiona “Saga” Staples.)
If you're interested in this stuff but don't have much time, jump straight to the "Conclusions from Testing" section in the last couple of pages, where two people analyze the results but come to different conclusions. Dave McCarty basically says EPH's positive effects aren't strong enough and the negative effects are too strong. Jamison Quinn (one of the creators of EPH) basically says that the positive effects are strong enough to be worthwhile, and that without EPH it'll continue to be very easy for a slate to dominate the ballot.
EPH is up for ratification at this year's WSFS business meeting; in addition, there are a couple of other proposed approaches that could replace or complement EPH.
I don't know what to think. i was initially skeptical about EPH, but the presentation last year won me over, and I became a pretty strong supporter (although I'm sorry to say that I totally dropped the ball after offering to help out with their presentation); but I'm sad that it doesn't have the full intended effect. I'm not thrilled with any of the alternative proposals, either, but I feel like we need to try something if we want the Hugos to be worth anything, because the Rabid Puppies aren't going away on their own anytime soon.
The other proposals for Hugo changes are in this year's agenda, including Jamison's FAQ answers about the new “EPH+” proposal.
Btw, today we voted to hold off on voting on EPH and EPH+ until Sunday, after Saturday's Hugo awards. The EPH folks are going to present, on Sunday, the results of what would have been on this year's ballot under EPH and EPH+, which will give us more info with which to make a decision.