I took a hot at this as well! Based on your idea and switch wiring but with a somewhat different fet switch. I used this schem
And here is the layout I drawn with the switching attached to the main board.
I also installed a tap-tempo from diy.thcustom.com/ and a expression pedal out for the feedback.
Here is the result
I also thought about using a switch to alter the expression out between feedback and delay, but I had the box drilled already and could't find the space for it. It would become a wild-wire-bonanza.
Anyway, not really something new, just thought I should share :)