it will be great if we can overlay a second icon on top of the Entity one. then the possibilities will be folds of what is offered in MDI. TV with WiFi, or BT … bulb, with flash to represent lighting energy … ideally we can control the size of the overlay icon and in which quarter to place it. however, half size (quarter area) on bottom right would be awesome.
after all it is all in the interface
I just had the same idea. Other examples:
- An entities icon + a small cog icon overlay to represent “settings” for that entity
- An icon + a small plus sign overlay to represent adding something
- An exclamation mark overlay for warnings
- etc…
Bonus points if we could give the overlay a different color! 
Would be very cool! Actually I tried to make it happen inside custom button card, but failed. Ended up with making screenshot of icon and using it as background and thyen displaying another icon on top. BTW my use case is animated washing machine icon that looks like that:
half-circle in the middle of picture rotates as washing is in progress.