It's the only announcement I'm excited about in the whole Nintendo Direct.
The only downside is that, for the moment, I don't really see the point of summoning crates rather than tables (or vice versa).
But summoning monsters to fight is so cool.
Crates are 1 block high instead of 0.5, and the number of triangles you have limits how many things you can summon. There will certainly be gratuitous echos though.