there is one feature (maybe these are actually two) that I am missing: An additional way of grouping related devices in the UI and switch them all in one go.
I.e. I usually do not want to switch on/off all lights in a room one by one, but in one go. Same is true for all the shutters in a room or even a whole floor. So the UI should not show all of those devices by default, but only the “group controls”.
However, sometimes I still want to be able to “zoom in” and control single ones. Obviously the “group control” may then have an indifferent/neutral state.
So this is kind of a sub group, but it actually implements a switch/dimmer/… and the UI would have to handle that accordingly. Question is whether all of the devices have to be of the same type (the the group control could be inferred and a lot could be done automagically) or if a mixture is allowed (then one would have to configure that actions one by one for every item in the group).