We did a fair bit of work on levels when @riban put together the status meters.
Trying to establish a ‘standard’ level seems to be fairly usage dependant, and proper implementation of Volume and Expression to incoming MIDI streams needs to be taken into account as, sadly, we aren’t dealing with the gentle analogue over modding but the cruel vicious digital world.
On the zynth we have established an effective patchable jack environment and with any such environment, the first issue is the context. Do we allow effects to assume that downstream input is of a correct level? certainly for devices that exist outside our inputs like Audio Input we would be foolish to not honour any standards that exist in those worlds.
Perhaps what you are describing might be met by an effects mapping applied as MIDI data? The ability to transfer system contexts via the zynth’s inter-control network would seem to be useful but, it’s turtles all the way down (and should be a snapshot). You still need to define a basic zynth reference tone, and from the audio in/zynth record/audio out mucking around I’ve done with an active guitar I have to say the level implementation is usefully good.
At the end of a day we put a wrapper round an engine and hope it plays nicely. It will be truly wonderful when all engines put Odb in the ‘right’ place whatever that is 
We’ve gained a lot of functionality with effects and it seems to be working and ultimately you trust your producing engine. If -10dBFS sits at green then I think the zynth’s work is done Zynth Peak Meter