This is a fair question. What I think will end up happening is that tiles will be de-emphasised for some purposes and will become more focused for others. You can consider the difference between push and pull:
- Push ? toast notifications / notification centre. A circumstance or entity requires the information to be surfaced to the user. A contact may have sent an IM or text, there might be an urgent weather warning, or a background download just completed. If important enough, you can show a toast notification (which can go to the notification centre if missed), else send it straight to the centre.
- Pull ? live tiles. The user will seek out the information when desired. You can provide a nice graphical representation of this information on a tile. Weather forecast, calendar agenda for the next week, news articles, YouTube videos.
There are also some other situations where one makes more sense than the other. A notification centre may be more flexible around interacting with notifications and displaying a larger amount of textual information. Tiles still allow features like deep linking, which allows you to pin a particular point in an application to your start screen ? your favourite artist, a YouTube channel, etc. And when there are notifications in the centre, you could still include a numeric counter on your tile to let users know.