A mix knob would be great for getting that effect dialed in just right and being able to assign it to an expression pedal would be another great feature. If you want to go crazy with improving it let us assign Wave/LFO and/or envelope follower to it as well as the Speed and other parameters.
Setting the Rotary to less prominent mix and having it seemingly have a mind of its own as far as its ‘rhythm’ makes a great AI band mate to play under the guitar part…
Nice idea. In the meantime this can be achieved by putting the Rotary on a different row with a Splitter/Mixer path and changing the mix value of the Mixer 
Yes please. I currently am running it in parallel split path and reversing the phase. It’s complicated but works well for me. If that was built into the block would be much better