Regarding the original question
The SCADA we use mostly, have functionality like: layers, decluttering, zoom and visibility according to zoom level, but I have not used them with the purpose to squeeze as much information/control as possible into a screen/picture.
In my opinion zooming and decluttering is only confusion and besides reduce the overview of the whole plant/process.
Show only what is necessary (or there is space for) and use animation like differente colours for differente object status. In addition use Pop-up windows (or moving objects/buttons in and out of the visible windows area) with commands and/or more information regarding parts of the plant/machines/objects etc.
Those actions can be activated with mouse commands like mouse-click or entering/leaving. E.g. pointing at a machine and a panel pops up (or moves in) with addition information/control
Making the window size bigger than the screen resolution (normally in the horizontal plane...) so one have to use panning or scrolling to move around the screen/picture has been done, but what if the operator have to watch the whole plant at the same time.
Or differente prosesses/windows?
A better solution is to use a video card with dual output (or quadruple) and use more than one monitor.
We have used up to 4 monitors. (If they wanted, they could play solitaire on one of them and watch prosess images on the rest...)
E.g. the next project is going to have 2 flat panels (front mounted), one with touch screen and one without.
Even if there is more than one monitor and mouse, there is still only one logical mouse...
If more than one person have to operate the SCADA at the same time, then clients have to be installed on separate PC's
So... IMHO I would have looked after a SCADA where you could position as many windows that you wanted, with pop-up windows, with many animation functions and scripts with mouse actions and possibillity to change object properties.
regards
BTW: The name of the SCADA is Factory Link from USData. A powerful SCADA but not necessarily the easiest one.