So I have been thinking a lot about how to make Tempo Rogue viable. In my opinion, the biggest thing holding it back is the inability to get past Sprint without losing tempo. So along those lines:
What do you think about a 4-1 charge 6 cost pirate with Battlecry: Your opponent's minions cost 5 more next turn. Essentially, this would help clean up the board and would only require you to deal with 1 turn worth of minions when you play Sprint on 7.
Alternatively, what about adding "Your opponent's minions cost 2 more next turn" to Sprint itself?