I hope it's not too late to submit an idea, I have nothing specific but just.. something I'd like for you to keep in mind while you design this pedal. My current two favourite pedals that I have ever heard or played around with (I only own one) are the Talisman by Catalinbread and the Deco by Strymon. One seeks to recreate the huge 7 foot sheet of metal that gave the beautiful tones of plate reverb which saturated recordings of the 70s.
The other is a tape machine, it does everything that you can do with a real recording tape deck from slapback delays, tape saturation/overdrive, flanging and doubletracking, all of the stuff that was only possible in post-production, now at your feet. Everything from Les Paul to the Beatles and Hendrix, every tape trick ever used is somewhere in here.
What the two pedals have in common is that they seek to give you that.. indescribable quality that is present in so much classic music, stuff that used to only be possible in a studio, and it puts them on a footswitch so you can use them in a modern, controllable setting. Rather than tell you what kind of pedal I'd want specifically, I want this: Something that gives your favourite recording that indescribable quality, put at your feet.
So think really hard, we have a perfect 'tape machine' pedal on the market, we have some amazing plate reverbs, the pre-amp circuit to the Echoplex has been done to death. Search your favourite recordings for that special 'something' and design your pedal after that sound. It doesn't have to be a classic recording either, it doesn't have to be limited to 'classic' music.