I've provided some custom CSS for this before:
[Feature] Follow specific topic and be notified when there is a new comment....
User is interested to follow updates on
specific topics only. He gets updates ( via email - e.g daily,weekly updates or notification ) only when there is a new unreaded post.
For example, he can click on
"follow button"to do that - something similar what you can do on Quora....
He can see what topics he follows in profile and manage settings there - notify me daily, weekly, monthly ...
EDIT just realized that there is something similar like
Watch is exactly what you've described.
How about pushing all the topcis you follow to an rss feed so you can pushbullet it to yourself?