You should say in the first post that you are working only for the N9 and Sailfish, but not the N900 ! :'( Few months ago, I discovered DebianKit, which aims to install a full classical Debian directly in parallel with the existing Android install. Since Harmattan is more or less a Debian and Sailfish is still GNU/Linux, maybe something like that could be achieved for using Android apps (in addition, if it works with Harmattan, we will be able to do the same on the N(eo)900).