So far Apple hasn't shown much enthusiasm for a convertible laptop or tablet. In fact, earlier in 2012 Tim Cook, Apple CEO, compared the idea to converging a fridge with a toaster - you could do it, but you wouldn't end up with a very good product. The general view from Apple seems to be that when you create a convertible device, you sacrifice too many of the good features of the originals, or else you will have to make the new product so expensive that few people will want to buy it.
However, the Windows 8 convertible laptop is already selling well, and if this continues Apple will probably have to think again. When users start to expect the convenience of having one device instead of two - and it probably won't be long before this happens - companies will have to cater to that. So i think we can expect to hear that Apple is launching a convertible laptop/tablet or some similar product some time soon, though they've alreay missed the Christmas 2012 market.