Bah, imo it's pretty easy to hurt Miracle Rogues without completely killing Auctioneer/Shadowstep/Prep/etc.
Make Leeroy cost 5 mana instead of 4. Hell make his attack 7 while you're at it, won't change much.
If he's at 5 mana, you can't ever shadowstep him twice, unless you have coin and keep it until turn 10 or so.
Using this, with 10 mana, the biggest combo possible would be something like
Leeroy -> Shadowstep -> Leeroy -> Coldblood x2 -> Prep -> Evis -> Prep -> Evis.
That does 28 damage - it's high, but it's 8 cards, which is almost impossible to pull off. If you still have an auctioneer on board it's possible, but it's a ton of work.
Otherwise, at 10 mana/4 cards, you get 20 damage, which isn't that bad, *and* it kills using Sap to get the taunter away.
The more normal situation will be Leeroy x2, which is 12 damage, for 8 mana and 2 cards, which is a bit more respectable, and while it's still a strong finisher, it's not as crazy OP as it is right now.
The problem with Miracle Rogue right now is that there are 2 counters - rush them down faster or make sure you always 2 taunts on board at all times. Just having one taunt forces them to do their combo at 10 mana (or I guess 8 if they prep the sap) if they can't remove your taunts, which is what you need to fill your deck with, and is kinda sucky because of Blade Flurry on a big dagger which is a crazy board clear. The thing is, if you always keep 2 taunts up on every turn, they're eventually going to be screwed, because they'll spend their mana on removing your stuff and slowly delaying the inevitable (their combo just cannot get in if you have taunts all the god damn time).
The problem is that you need to build a deck specifically against that (why else would you run all taunts???) so you're screwed against a lot of other stuff.