I think it's more fair to say that making things that should/could be OS features isn't a safe way to make a living. Or if you do want to risk it, just be aware that you should have a fallback plan.
Just started using OS X heavily at work on a large monitor and started to notice a bit of a window clutter problem. Your app looks like it could be the ticket!
How is a to-do app "should/could be OS features?" Or a camera app that uses the volume button? Or Instapaper?
I don't think there is an obvious way to tell what Apple has in their roadmap. Specially when they publicly downplay the importance of some features only to implement them later. Maybe they should make their roadmap public? :)
