I think HDDs days are numbered as an OS drive, and if you want a powerhouse of a system then an SSD is a must as the OS drive, otherwise an HDD as an OS drive is just going to severely bog the system down.
As for storage, HDDs are still here for a good few years to come for storing large amounts of data, be that video or audio content, or pictures and documents.
As for this new HDD technology, sequential read/write speeds will probably improve, but i can't see this technology cutting access times or increasing random read/write performance, and that is where SSDs are untouchable at the moment.
A lot of people think that only application loading times are improved by an SSD. It goes much deeper than that, and is something i will try to address in an upcoming SSD review.