Is Apple gonna come out with a MacTablet? Uhh, you're a little late. They already made one, the amazing Newton!!!!
Ok, seriously now. While a tablet would be an interesting product, I personally don't see it getting much of a following, especially not from Apple's current demographic. Just look at Windows tablets. How many of those do you see on a regular basis? I've personally seen maybe two or three used by people, two of which were business type people and one was actually one of those notebook/tablet contraptions (and to be honest, the girl just used it to doodle on).
While tablets are an interesting concept, I just don't see them as being very practical, and as a result, not a very compelling buy. If you made one of those notebook/tablet hybrids, then maybe you'll get more buyers. The only way Apple can make sure it doesn't fail if it goes down the hybrid route is to make sure the thing isn't underpowered and overpriced, much like the PC versions are (another reason why they've failed to catch on, you get more for your money by getting a regular notebook).