At least in the Xperia X there is kernel 3.10.84 (accidentally the same kernel series as in RHEL 7 ).
Still, for long life after official support ends, would be marvelous if Jolla provided 4.4 kernel working, so that community would be able to support it for long time after.
Yes currently 3.4 kernel's don't work, but with enough patches it should work.
Google Play store downloading does not work anymore even with Jolla 1, apparently due to Google's changes that block unauthorized devices.
SailfishX 2.1.3.5 uses Linux kernel version 3.10.84 compiled without btrfs support.
For example, backupping the entire home directory in a single Linux command (needs ssh enable in SailfishX developer settings, I also set up a fixed IP address to have "xperiax" hostname in /etc/hosts
Can anybody who has gone through the installation tell me how much hardrive space is required?