This idea comes from a studio engineering perspective...
I think it would be cool to have a plugin that has a variable phase adjustment from 0 to 180 degrees. (also a polarity switch)
I think this can be achieved with a delay that can do as little as one sample length and as long as whatever 180 degrees would be for 20Hz...
This will give some very interesting sonic possibilities with adjustable comb filtering.
Also help with any possible phase issues plugins may create if they are being blended.
Just an idea.
What do you think?