The outcome of not testing if $scene is an InterfaceController is probably ok 9 times out of 10.  If $scene is actually a defined insteon device, this code will make that device a controller, which seems fine.

The only oddity, is if $scene is not an insteon device, such as some other random device supported by MH, the outcome of that is less clear to me.  

I don't have a simple solution and I think the likelihood of a problem arising is very small, so I just left it.