Our instructors at the University of Agder in Norway were used to telling their students to put a bin outside the students group room if they needed help from the instructor. They wanted a similar behavior in Canvas. One could argue that this is a better solution than having the instructor subscribe to all the group discussions, especially since an instructor might have many groups in large classes. But being able to do both things in native Canvas would of course be best.
We solved the “bin” feature using custom js/css in Canvas. It is a small piece of a larger open source custom Canvas design which is desribed here: http://matematikk-mooc.github.io/
The images below is taken from a students group discussion view. When the student group needs help, one of the student presses the "Tilkall veileder" button (notify instructor). This in turn leads to the steps shown below.