Well, this is a very common question.
Yes, DD 2 will have multiplayer, probably the players will host the servers and nobody will pay.

How can they keep the same engine if the game will be in 3D?
There will be a completely new engine. Although from what I saw in <img src="/ubbthreads/images/graemlins/riftrunner.gif" alt="" /> (which is not DD2), the 3d characters look very much alike the 2D ones in DivDiv.