A hybrid meta/audio device. It reads the audio input volume the effect receives, converts it to slider values (it will need a decay parameter), and routes it to any slider in the effect chain, similar to what the LFO device does.
Example usage: Record the guitar, add it to a track. Add this device to the signal path, then the filter afterwards. Then make the input volume controll the filter frequency. Viola! Auto wah.
Imagine how many other ways this device could be used.
Morph device. Many synths allows you to route a single slider to a lot of different parameters at the same time - this allows you to do very complex things by just moving the morph slider. Would be nice to have it in form of a renoise meta device.