4 years ago
The problem is not Mint, it is Skype that (deliberately?) works quite poorly on any Linux since Microsoft bought it.
As far as I know the Skype will not work with microphone until you select the INPUT device (in case if you want to use logitech camera with built in microphone and there isn't any on the motherboard). Selecting at boot using the same criteria as after plugin or unplugging the device. Turned on manually would leave information for future events (restarting, unplugging and plugging back) don't see a problem. Anyway in mint 18 there's a bug with using microphone build in to camera. It does't keep the selection when closing window.
Applications choose in and output devices and this is not something that the OS can decide. And rightfully so.
While your idea may seem good at first glance there are many issues with it. Did you consider start order at boot time? Or devices turned on manually in different order?