This is a good idea but your title makes it a bit confusing. A multi-effect chain might be a better name perhaps? Quad makes me think of a surround 4.0 setup.
I actually have a topic that’s quite similar to this Plugin chainer/ Macro control - #5 by keyxmusic - Cubase - Steinberg Forums
KHS: it doesn’t have to break anything in the current system. They just need to introduce a new plugin that loads other VST fx, and is capable of optionally band splitting. This will also fix a problem in Cubase, where you can’t load multiple FX chains on a track. Everytime I want to do that, I have to route the track to an empty group and load the second FX chain on the group. It’s possible but not the most elegant.
Also, because it’s not the way hardware works doesn’t mean we shouldn’t/ can’t do it in software. If I could cut down the track count from 1 track and 3 bus channels to 1 track with 3 multi-effect chain on the insert, I’d do that in a heartbeat.