I just had a random thought of giving observers ability to ctrl+num units like how normal players would do. It would be useful for observers to remember important units and quickly give attention to them in different time and space within a gameplay. I can see it being only used in official tournaments, but observer mode is mainly used for that anyway.
Main use would be numbering shuttle, arbiter, dark templar, etc. I am not sure how useful it will be but hey ho I had a thought and why not share it.