"Another 10 years" for WoW? No way. Not without a graphic overhaul.
Blizz has been doing small graphical updates over the years. It will never be bleeding edge obviously, but if you look at a screenshot of WoW from 2004 and one from MoP there's a huge difference.
One of the reason WoW's subscribers have dropped off is the latest expansion, Catalcysm, sucked. It was really hard early on and there wasn't very much to do at max level, which made a lot of people leave. MoP however, has a ton of new stuff for max level, it's definitely their largest expansion to date, and I bet it will being a lot of people back.
I don't think a major overhaul will ever happen, and it's not really necessary, they've been slowly updating things like water, cloth, and the models look much much better. Look at the Human race model compared to the Pandaren race model, there's a huge difference in quality.