Can somebody explain to me why we are using the 4.4 kernel when there are new ones for this device? Are they not stable enough or is it something else?

Looking back at the MWC2017 with the official support from Jolla for SailfishOS, I'm guessing it will become even easier to port whatever on this device. Don't have it long enough to tinker with it, as I need a stable device now and only installed the concept branch, which is okay for now.