Actually, we already have a 3D Gamemaker trainwreck - behold Eyeball 3D: Maze of Felsh.

FWIW it's almost nothing like Klik & Play. KNP is more about giving you a blank canvas (and some premade graphics which are optional) and letting you script your behaviors however you want. 3D Gamemaker is more about having you make choices a la carte. It's quite limited according to Sergio, since you're pretty much restricted to the predefined behaviors. Sure, you can import your own models, but even that has issues. Level making is more or less Wolfenstein-esque. Might be fun to mess with but don't expect too much out of it.