I am an end-user of Discourse’s forums (not from @AquaL1te 's community though) and have been wondering the same thing, as i don’t always keep my apps open and usually browse forums once a day, twice a day at max.
A single email regrouping all of today’s notifications would be a perfect fit for me. And i’m sure, for many more users, who hope to find in forums a slower-paced, better argued conversation than with instantaneous chat apps.
The solution you give here would require admins tw manually edit this setting for the whole of their users. Please give this power to users, let them decide how they want to interact with the forum they created an account for.