Hearthpwn

I think it isn't really that much of a concern if Y'Shaarj, Rage Unbound pulls out something with a battlecry just because of how many raw stats he puts on the board. Changing out cards with battlecry/choose one effects just for one card which isn't even the sole win point of the deck probably isn't a very good idea since the cards currently in the deck are much stronger independantly than the ones you proposed.

Its sort of like when Varian Wrynn was announced and people thought it would be a good idea to ruin their entire decks for the service of one card. The problem with Varian Wrynn never was that he canceled out battlecries.

C'Thun is interesting but probably not worth the deck space since if you're running cultists sparingly then he's only ever going to be slightly better than Ragnaros the Firelord at best and most of the time worse. 

2 x Blood of the Ancient One I think would also fit in really well.

That would probably be a great Idea is Blood of The Ancient One wasn't poopy doodoo garbage.