Even at 8 Mana Bonemare delivers insane value. 5/5 plus buffing a minion with Blessing of Kings is probably still pretty good. It might indicate though that we'll get other 7 or 3 mana cards in upcoming expansions that are not supposed compete against or interact with Bonemare.
+1 mana is bigger than some people realize. Call of the Wild used to be 8 mana and was in every Hunter deck, now it's 9 and how often do you see it?
The difference between 9 and 8 is huge unlike the one between 8 and 7. 8 allows you to use heropower, while 9 mana prevents you from doing anything else in the turn. There is almost no difference between 9 and 10 mana. For 10 mana, Call of the Wild could be played with hero power, allowing 7 face damage on top of a decent board. The nerfed reduced the face damage by 2.
This Nerf feels like a direct attack on the free to play player base. At 7 it was an auto included if you didn't have any good class rares/epics at 7. At 8 you are stacking it up against amazing cards like ironbark, al'akir, tyrion, primordial drake. As well as pushing it behind the curve of several game ending or board clearing affects making it an 8 drop 5/5 without taunt. Far too late.
I think if that card was rare/epic it would not have been nerfed, but I might be wrong I believe this is the only mid/late game neutral common to ever get nerfed?
Is this also a priest nerf in disguise because now this will appear as a worst possible Free From Amber choice
Fungalmancer is the new Bonemare for aggro/swarm decks anyway it seems. I dropped Bonemare from my Zoolock for it and just tried Aggro Paladin on my Asia (arena/dailies only) account, still running patches (can't afford the murloc deck yet there) and it won 5 out of 6 games in about 20 minutes (low ranks though, went from 17 to 15 in those 20 minutes, rank is low because I only do dailies on the account). The only match I lost was a mirror match, lost the board by turn 4 leading to a concede by me, game took about 2 minutes ;)