If you look at something more recent and concrete, like the sudden indie program MS has, we can make better guesses. The general assumption was that MS was using their Windows 8 partition in the Xbox One to run those indie games, and although MS is saying that won't be the case, it's not a bad idea from a technical and security perspective.
If Sony wants to do something similar, where anyone can run their own code on the PS4, they can consider something like having the Android libraries running in memory with the memory and CPU that's rumored to be reserved. The controller already has a touch screen that seems to be designed to work with touch-screen enabled apps.
I think that's the kind of thing we're talking about with the memory reservation. Not a single feature so much as an entire separate app (and/or game) ecosystem. Doesn't have to be Android; could be Playstation Mobile (likely, except the SDK is useless for apps), could be OtherOS again, but running in a VM with a Sony-supplied BSD kernel, or something completely different. Or maybe none of those. But the point is they're reserved enough space so they could.