Idk how your backend works. I'm an OS guy. Rewrite it in C, and maybe it could handle it.
It's not really a matter of the language used.
It's just a query on the db to check if a comment/post replying to you has a pending notification in your PM box before you cast a vote toward it.
Edit: I added it as an experimental feature. I'll wait a few days to see how it's draining on resources.
(post is archived)