Someone will produce a good product in the next 18 months. It's not rocket science, and there's an enormous pile of money. But adopting Apple's integrated model is a) not a sufficient condition and b) very threatening to existing business models. Apple's monopsonistic position w/r/t componentry is also going to mean that whoever intends to compete is not going to be able to do so on price, the traditional domain of the PC competitors.

I'd expect the best competitor to be a hail-mary type of move from a dying supergiant (Samsung?), and the most successful to be from Amazon.

Standard disclaimer: former AAPL employee.