Show number of selected objects
It's amazing nobody asked for this.
Just use that bottom filed that can show artboard name, current tool, etc, for saying how much objects user has selected.
If you are as lazy as you are implementing user requests — make just this. But make it better and allow this field to show several things instead of one. And add artboard number there.
As per the comment, this value is available in the Window > Document Info panel, when Objects option is picked in the panel’s flyout menu
This is an old request, and maybe I'm misunderstanding, but I believe you can find this under Window > Document Info, then click the flyout/hamburger in the upper-right and select 'Object' ...I keep that open all the time. Very useful.
Wilzon Osadia commented
I know right, it seems like a very useful tool to have??
did you figure out how to know the number of objects?