http://crytek.com/news/crysis-2-ultra-upgrade-with-the-directx-11-available-today-for-pc
Above is the proof that sandbox is coming Wednesday. Read second paragraph

Ok, this announcement is exciting and all but unless the following question is answered, I will not be satisfied:

WILL USER-CREATED MAPS BE PLAYABLE ONLINE w/ OTHER PLAYERS?

^If the above question is answered yes then woohoo. I can continue my blueprints for my multiplayer map.

if not, then what's the point of releasing the editor!