We already see the value in responsive web design, which is also in it's infancy. Eventually, we will have responsive operating systems, applications, and maybe even hardware.
Far from it. I've been watching major companies try to converge them for 20 years, all to abject failure (tiny niches aside). The iPad succeeded precisely because it avoided "convergence".
But because it's successful, there's a big enough market to develop apps and accessories to make it do all the things it wasn't designed to do.
Basically, the iPad succeeded because the technology behind it had finally matured, and Apple paid close attention to all of the mistakes that were made over those 20 years.
I may be wrong, but only time will tell for sure. Right now we are still in the phase where companies creating hybrid devices are making a lot of mistakes. I'm betting that someone is eventually going to get it right.
In the PC market there is more overlap, with pretty solid $700 minitowers, but again the minitowers imply you will pay for the electricity and performance with a cost in size and portability.
Long term ... sure maybe a 12 core tablet is possible, but that is really long term IMO.
I'm not saying that a perfect hybrid will exist in the next five, or even ten years. I'm just saying that it will, because it's the obvious direction to go in.
Right now, creating such a device requires a significant amount of compromise, but in the future it may not.
The idea that such a device can't exist because all previous attempts have failed strikes me as short-sighted.
Rather than One True Device, it may make more sense to have different devices for different jobs. For example games consoles and e-book readers are devices that sell very well despite limited use cases.
I can see advantages to perhaps having many cross platform libraries to allow developers to reuse application logic across devices.
As an example, responsive design allows small businesses that may not be able to afford to build multiple versions of a website to instead create a single site that provides multiple experiences based on the type of device used to view it. Users win, whether they care about it or not, because they can now use the site on the device of their choosing, without worrying about it being functionally broken.