It would be a great feature to be able to select your own icon for a device. Especially for switches, sockets, sensors, etc. it would help a lot to be able to select an icon from a library to show a visual that displays the attached device/appliance or for instance a door or a window.
This would, in my opinion, improve the usability of the app’s a lot as you don’t have to read, but in a room of the house you have an immediate visual display if the items connected and available. Especially for receivers and senders that are mounted behind lights and switches and plug in sockets the current icon that is displayed doesn’t improve usability.