I've come across situations where changing the hierarchy of the filter structure during recording would be useful. Is this possible with current tools, or is this one of those efforts where a major change is required?
Anything you can do can be done while recording. It doesn't care. If you want to reorder them, just go into the list and click the arrow buttons. Change a setting? Same idea.
The question to consider though, is, "How does it look or sound while things settle into their new configuration?" For some things you hardly notice, but for others it can go way out in left field before coming back into something sensible. Reordering live is not normally done in professional rigs, so consider why you need it for yours.
Usually, instead of reordering, you'd just have multiples of the same thing, so by (gradually if needed, to keep it sensible) setting one out of the way (do nothing) and bringing the other in, you've effectively changed the order. But even *that* is rare. Most of the time, the processing settles into something that stays put, with things that do nothing completely removed, and you just tweak the volume after all that, or switch scenes.
If you need to switch between two different sets of processing for the same signal, then you split the raw signal into separate processing chains, and switch between the results of those separate chains. The chains themselves stay settled as they are.
I also think there could be a major reduction in HotKeys by being able to set any (or certain) hotkeys with a toggle function. I realize that HotKeys, like start and stop recording, are by definition two way, i.e. do and stop doing can act as a toggle. But I'm thinking in terms something a Fade In and simply the press of the hotkey would undo the action exactly (a do and than an undo :). Any info out there?
The Advanced Scene Switcher plugin might get you at least part of the way there, if not all the way:
This plugin will allow you to automate various tasks using "Macros". Macros consist of a list of conditions under which a list of actions will be performed. Examples and guides can be found in the wiki. Feel free to contribute! If you run...
obsproject.com
The name is a bit of a misnomer now. It grew out of the Automatic Scene Switcher that comes with OBS, but has become a full-blown automation hub! It can both send and receive hotkeys, trigger on and control audio, adjust filters, trigger on and switch scenes, run external programs and scripts, etc. and so on...
I've long seen Adv. SS as its own programming language, that is probably Turing-Complete, which means it can compute absolutely anything that can be computed at all, given appropriate access to the data, and enough resources and ingenuity to make it do what you want it to do.