I think, with the announcement of the iPad, we can see the direction Apple are headed in with touch devices: Give it a custom OS, do away with multitasking & charge way too much for it.
Maybe one day this could happen but it would likely be a very costly add-on available during order or a new product line altogether.
That said I wouldn't complain if my MacBook Pro sported a touch screen but I doubt that I would get much use out of it unless the screen could fold. Otherwise I would be worried that I'd break the screen.