Right now there's no way to watch, for example, all cards that end in +discussion.
There's some question about how to design this. If we make it so that Search cards with your name in +*watchers are interpreted as you watching the cards the Search finds, then there's no way to watch individual Search cards (the same way that currently there's no way to watch individual Cardtype cards).
doubt we can do this with just any search, but we could probably do it pretty easily with Sets
make notification work with Searches+discussed in support tickets
make notification work with Searches+relevant user stories