OMG I would sooo use that everyday!
Especially if we could change thigns like the textures used in order to simulate lava, rivers, sewer/sweage, chemicals, ect
Imagine adding some particle emitters that move around as they randomly emit particles
^-- now you have bubbles, fog, steam, rain/acid drops, ect
EDIT: Also imagine if we could specify the Y vertical positioning for things like waterfalls and lava falls -or- water/liquid going out of a large pipe and draining down into an open pit that is larger than the drain width.. would look way cool, eh?