Reaper supports plugins written in JS

http://www.reaper.fm/technical.php

Voxengo's Impulse Modeler sounds similar to what you're describing.

http://www.voxengo.com/product/imodeler/

This seems like the closest - from a UI perspective. The screen shot indicates the ability to design a room in 2D (rather than 3D). App appears to be windows only and closed source.