The CPUs run different OSes and there is no ability to move tasks between them; this is rather unlike a hybrid or "big.LITTLE" approach.
Thankfully Intel has already done alot of new work in this area - allowing PCI devices (GPU, Xeon Phi) etc, to share computing resources more evenly.
Definitely going to complicate things but it could easily end up worth it for a laptop if it can reduce power usage to almost that of a phone when not doing anything particularly demanding.