What native extensions? Android native code is just regular ARMv7 (usually) that links into a stripped out libc called bionic. Since both Android and Jolla are Linux there should be no problem with portability.
The big issue for compatibility is in the Google Play libs - Amazon devices have similar problems with maps and that.
Seems like BlackBerry 10's Android Runtime had this exact limitation but is now being improved to address this: http://www.theregister.co.uk/2013/11/25/revealed_how_blackbe...
I wonder how they both compare.