Not 100% what you’re getting at, you mean like making it possible to “automate” a tool slider/rotary?
Some viewbuilder controllers you can actually bind directly to internal renoise observables, with the bind parameter if you want two way communication without gate checks, for some reason. I’d suggest it’s often most practical doing it via your own custom observable, so you can attach any notifiers you want to it. A little bit depending on what kind of ‘duplex’ and functionality you need.
Also… even though value changes are “realtime”, they are also linear/sequential in one way or another. So, for example, you might (likely) find out that a note-play has already ‘happened’ when an automation point is happening which in turn tries to change the note in the pattern editor - a little too late.
EDIT: but yeah it’s a little bit interesting. Now, if I remember correctly you can’t access doofered devices freely and attach notifiers to them (? might be wrong, don’t torch me). Otherwise I’d imagine something like making a neatly packaged doofer that thanks to clever formula devices and notifiers does very specific/custom things to some instrument or phrase parameter/mechanics. I don’t remember exactly everything that’s possible with Renoise, but I’m keen on checking if you could theoretically play a proper chord with phrases and something like a “2147” effect on just one root note.