It would be great to be able to select (filter) the range of frequencies that are affected by an stomp or effect. It could be done by simply selecting the starting frequency and the ending frequency. Everything in between goes through the stomp or effect while all content in the other frequencies remain unaffected.
It could be used on the loop FX as well so we send to external stomps or effects only the frequency range that we want to be processed while the remaining ones are not altered in the signal.
With this feature we could achieve things like combining a distortion stomp for the low end with a fuzz for the high end before the amp, a phaser on the mids with a chorus on the high end or simply combine delays and reverbs in different ways.