With phones and tablets you could probably say that a majority of the market is already touch-oriented and that the next step is merely for the technology to spread across the market. Microsoft have been looking to touch screens for a while, such as with Surface, which is basically an interactive coffee table. Surface isn't merely a multi-touch screen, but one that can recognise objects that are placed on the screen.
Desktop touch screens exist, at a reasonable price for an enthusiast. If it's something more than a novelty, then there will be uptake progressing into mainstream consumer markets. However, we know what touch screen interfaces can do and we know that in some applications it's everything. What matters is setting the interface in place before anyone really needs it.
A touch screen interface simply won't work without a touch screen and it won't be enabled by default. For most people this is going to be like the improved speech recognition in Win7; they won't even realise it is there. The Windows devs don't have to do any work to reproduce the interface they've been using in 7 and Vista, but to lead touch technology into new areas? That's the real work.