secrets

Not planning on it for the near future, no. I'd totally encourage you to try though, there is no better way to learn than by doing things yourself.

A quick tip though, I wouldn't recommend that you make a system that subscribes to "everything" - I would try to make something more component based. You could create a trigger component that knows what notification(s) it wants to listen for. In Hearthstone a secret is only active when it has been played, so it would be easy for the system to merely listen for the play event of a secret, parse it for the trigger component(s) and then register for the notification(s) that are needed. Haven't thought it through completely but maybe it can give you some ideas to try out.