Technically, there are some apps that can do that, I believe, but there is no rumors regarding native printing support, so any speculation at this point is just semi-educated-at-best-guesses.
The way iPhone does printing is through the special AirPrint stuff which required a specific compatible printer, but its something. So its sorta printing.
My guess is that it'll be a while. couple years?
Needless to say, outside of the supposed merge between Windows and WP, I dont think we can expect full-on USB, Wi-Fi everything printing.