Not a complete solution, but the Advanced Scene Switcher can already do that detection:
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
It does not do VISCA (yet?), but one of my rigs has it call an external utility that I wrote to do that. Thus, controlling PTZ's from Adv. SS.
Another of my requests - OSC (Open Sound Control) - did become native, so there's a chance that you could get VISCA added to it too. Post this on the Adv. SS discussion thread, and see what happens.