Wether Ohmnom is going to be viable depends on decks ability to abuse floating green mana more than his ability to grow. Say, in Rock shell, you can keep 3 mana floating and if you run into geddon just cast Witness for land. In decks playing some sort of reanimation he can serve as a backup plan, allowing you to hardcast some tough stuff. Also note that you can float mana, swing for 3 and than use the mana to cast spells on post combat main phase, so it is not like you need to waste turns to grow him. He is still at most medicore in current decks, but ability to accumulate few turns of mana in one turn (while swinging for good damage, or keeping enemy goyfs at bay) is good and can find his uses in future.