I don't really like AMVs, anime or otherwise. But this...
This is perfection.
Honestly. You slap a title card at the end of this that says "RWBY: Volume 4: Coming this Fall", maybe a slight dulling filter over it to make it a bit washed out, and this becomes the perfect teaser trailer showcasing everything that is awesome and exciting and thrilling about the show.
I have never been more pumped for RWBY than I am right now. And that's saying something, given that Volume 3 pretty much killed me and my drive.
By the way, this should be obvious, but: massive spoilers for RWBY through Volume 3. Seriously. Nothing is sacred here.