[persnickety]

I'm not sure I'd call anything using libhybris "Linux-based". Their low-level elements come from Android with all the problems that implies, including Android being Linux only in the most irrelevant technical sense.

[fractallyte]

Sailfish is based on the Linux kernel, and Mer, which itself is a fork of MeeGo - a mobile Linux distro.

Hybris is just one component that Mer supports: a compatibility layer which allows the use of Android libraries and drivers. But that doesn't make it the backbone of Sailfish...

[persnickety]

I'd say those drivers and libraries are the backbone of an OS. Everything else is on top of them.