This would be most useful when playing with mods that add over 9000 different resources and mid products. also for beginners I believe it would be good in base game too.
There seems to be a lot of room in the UI for the content information. I believe it would easily fit there in text form. See picture below for example:

I have clicked on a piece of transport belt. I would like the pop up window to show contents of the belt in question. I am also mousing over a different piece of belt. I would like the contents to be shown on the right in text form.
What I am doing right now to overcome this is that I sometimes deconstruct a belt just to get the text pop up about what resource I received by destroying that belt. Not really ideal.