I love SE's newsletters, and I love going through the hot network questions. There's always something interesting, if not fascinating being asked and answered.
Basically, there are newsletters for everything, except the hot network questions. I bet a lot of people who use SE's various communities are interested in discovering new things, increasing general knowledge and generally observing what's going on.
A Hot Network Questions newsletter would be a perfect solution to satisfying that need. Let's go beyond the ancient RSS feed and make this an inbox darling.
I know there are solutions but an official service just seems lacking.