Apparently because it has "Block discard support", which among other things improves wear leveling on SSDs/flash/etc.. It does have SSD mode as well which does a few things to level wear. Apparently everything is about leveling wear. Like I said before, it's weird that they chose it. My kernel is 3.10+, and look at what it says: I mean.. it isn't so much of a problem if the format isn't finalised (assuming they are versioning it ;-) ), as migrating to btrfs is pretty straightforward. Still, I didn't have the courage to test it myself, but loads of people out there are using it. I guess I'll start testing it with my Jolla [when it arrives]!