I made 3 changes to the deck today and have played about 5 games so the sample size is small.
The first change was to substitute Revenge for Whirlwind. There was 1 game where the 3 damage was helpful but other than that it's basically served as a 2 mana whirlwind.
The second change was changing out Kezan Mystic for Nefarian. Nefarian won me a game against a Paladin with Lay on Hands and Muster for Battle. He didn't help against a Druid when I drew Poison Seeds and Recycle. I wanted to see what his fun factor is like and I was ok with adding another big guy to the top of the curve if I was going to have an extra spot. He definitely is fun but that's probably because he is new. He's got potential, but the Mystic is more valuable against Mages and Hunters. On days that those 2 classes are 50% of your opponents (which is a lot of days) you'd probably be better off with the Mystic. I think Kezan will probably come back once I've had my fill of Nefarian. If there aren't many secrets out there I'd probably consider subbing her out for something like Baron Geddon, or another big "threat". It's nice to have more early game options but if you don't curve out well or mulligan really poorly, having a 4/3 for 4 isn't going to save you anyway.
The last change was subbing Thaurissan for Sylvanas. In the few games I played, I was happier dropping him in situations than I would have been dropping Sylvanas. I felt like my opponents generally treated them similarly - requiring attention right away. That has meant trading several of their minions in to it, burning some premium removal, or using a silence.
When trading their board in to Sylvanas, they could usually engineer a way where I'd end up with a 1/1 or 2/2 type minion, or occasionally have to take a gamble that I'd get something bigger. I have been happier with the result of my whole hand being discounted more than I have been with the result of Sylvanas' deathrattle going off.