I personally think that parts of it are April Fool's jokes (IE- Horse, Removing Fishing, Diamond Chickens, Exploding Animals, lots more) and some aren't (IE- Colored Glass, Some new worldgen, and I honestly like the chickens attacking you, lol). Like hidden hints at some stuff.
Possibly hinting toward things for 1.6, or actually for a 2.0. I personally would be disappointed at mojang if it is 100% a joke, as it looks like quite a bit of work went into making it.
