Egosearch is very useful as are feeds, but this is about combining them.
But at the moment you can only use feeds per forum or for the whole forum. A personalised feed for each user (that would require http auth) could be extremely useful.
Each user would need to use http auth, and the url would be customised. Like it is currently done on github for the user's feed.
It would, check the auth is correct for the user and then that user logging in matches the person the url is for (perhaps userid or username on the end of the url), then fetch the egosearch list, check those topics and post the latest replies to those topics in the feed.