Sony last year announced their intention to "mainline" their Xperia devices (their main phone brand)[1]. This could eventually mean running Android on the latest mainline kernel, and perhaps even GNU/Linux[2].
[1] https://developer.sonymobile.com/2016/02/17/work-on-the-main...
[2] Jolla (developers of SailfishOS, a real-Linux-on-mobile OS) announced in February that they are partnering with Sony to bring SailfishOS to the Xperia X (https://jolla.com/wp-content/uploads/2017/02/Sony_Jolla_pres...), which should hopefully be out this month. It's taken a long time, but real-Linux-on-the-mobile is getting closer.