It would be nice if this could be picked up even though it is old. It's a very useful feature for understanding config changes easier and it should be a relatively small effor.
I'm currently working on this and the recent idea would be a sticky textbox next to the configure page (see picture). "Really mandatory" fields are not possible as far as I know, since the user may just ignore the red errors/ warnings and click S_ave_ nonetheless. It is possible to display an error/ warning depending on jch plugin configuration or to just always display it.