If you're adding new a class, it needs to have its own spin with different abilities. Like what new hero power you could add on the most basic level that makes sense and it's balanced against the field? It far too difficult to make anything new now, the best they can hope to achieve is manage the existing 9 classes to be more in line. BB already confirmed that they're not even thinking about new classes.
Man I can think of like 10 hero powers while taking a dump on the toilet seat. Other people have already done it when coming up with the various Monk/Death Knight classes.
*2 mana: Summon a 1/1 minion with Charge that dies at the end of the turn (it can't attack heroes). The Boar is a 1 mana Beast with Charge, make it ethereal, can't attack face and no tag (well the tag can be class exclusive) and it's roughly 0 mana in power level.
*2 mana: Deal 1 damage to a minion and give it +2 attack (so like 0 mana Inner Rage which is balanced because Mage has "Moonfire" as an ability which is also 0 mana)
*2 mana: Return a friendly minion to your hand, it costs 2 less. Shadowstep but costs 2 mana so balanced.
*2 mana: Give a friendly minion +1 Spell damage and reduce its attack by 2. I think just giving a minion +1 spell damage is too powerful so I put a drawback on it as well.
*2 mana: Equip a 1/1 Weapon that heals for 1 HP when it attacks. Sort of like the Druid hero power but you have the heal effect and if you buff up the weapon you can keep getting heals off of it.
*2 mana: Summon a 2/1 that dies at the end of your next turn. This is like an upgrade Paladin hero power but the minion doesn't last forever like the 1/1.