I would expect 10 speed road to stay for a very long time. 8 speed still exists in Shimano's named road groups, and that appeared a long time ago. They can't add too many more speeds to the rear end of the bike before needing a major redesign of the standard road bicycle's rear triangle and rear hub, which is not going to be as easy a transition as previous group upgrades have gone.
Now mountain drivetrains are another thing. With 142 thru axle, and the popularity of 1x, I bet we see more gears on mountain cassettes soon. 8 speed may only stay on walmart bikes.
Edit: 9 speed users only have to use Ebay if they're looking for Ultegra or DA grade stuff- Shimano still makes plenty of 9 speed hardware. Heck, Shimano may still make-or still possess a quantity of- light 9 speed cassettes (they still have some older stuff that isn't posted on their website), but I doubt many stores would keep such a thing on the shelf.
Last edited by Raiden; 11-30-14 at 07:10 PM.