I made a post about this a while back. I main Shyvana (jungle) and can definitely say that she needs a nerf. But this is too much too fast; the dust from the devourer nerf is just starting to settle now. That alone isn't enough of a nerf, but I definitely think its over the top to hit shyvana with 2 early game nerfs (where even small changes have dramatic effects) at the same time.
I'd like to see the W nerf go through (its extra damage) and leave the Q alone, at least until we see where that leaves her. Early game buffs hit hard and should be looked at carefully, it doesn't feel like this is being done here. The Q nerf is devestating; not only to jungle shyvana but lane shyvana as well. Its also incredibly punishing; you don't make it back to the same amount of damage until level 12 (well into the mid game) making this a massive nerf against champions; somewhere she really doesn't need the nerf. As a cc-less champion, Shyvana needs her damage to stay relevant. That is why, even if they do go through with a Q nerf, I'd also like to see a cool down buff to balance out the ability; make it less bursty but make the sustained damage (if Shyvana can actually stick to her target; her intended weakness) the same.
I suppose we'll have to see how it goes though. I am definitely nervous that these nerfs are going to knock Shyvana out of viability and she is gonna get left there for a while. One this is clear though, any buff to top shyvana is going to buff jungle shyvana, so i doubt we'll see it.
To be honest, I don't even think devourer is that big a problem; it has weaknesses, as do the champions that use it. With the exception of Shyvana (who does need a nerf) there are no devourer junglers doing particularly well until you get to Yi (ranked 13th) who is also getting nerfed due to an abusive build path (not devourer, but off tank). I guess what I mean is that devourer junglers aren't dominating the scene in a big way (not like Feral flare was at all). Overall I think the item is okay and has given champions who wouldn't otherwise see play a place in the game.