Samsung confirmed the development of Heterogeneous Multi-Processing (HMP) yesterday and ARM has now posted few videos showcasing HMP's capability. The videos show how Exynos 5 Octa 5420 can use all or some of the cores, which in this case, they run QuickOffice and Angry Birds Rio. The third video also shows how big.LITTLE can work alongside the Mali GPU.
One thing to note in these videos are the use of 5420 SoC and not the first Exynos 5 Octa 5410. This could mean HMP may not come to the Exynos 5 Octa that powers Galaxy S4. This is just a speculation but highly plausible at the moment.