It's not, it follows the upstream releases and has a couple of patches for the Surface drivers (e.g: SAM) that will hopefully be upstreamed one day. They have something like ~50 commits on top of the release tag [1].
The main developer is doing an amazing job, and the fact that Linux runs on so many Surfaces devices, including the ARM ones (like my SPX) is just amazing.
Linaro (Bjorn Andersson) helped quite a lot in the Linux on ARM environment, and qzed (Maximilian Luz) is doing all of the Surface reverse engineering and kernel driver in their own free time.
Sorry, I had to downvote you because this is just disrespectful on the amount of work awesome people are doing on their free time, and you clearly have no clue on what the linux-surface project is about.
it's the same sort of hacks from teenage Android community to port binary blobs. if you're not familiar with that, just be glad.
in summary, old unpatched kennels with weird binary code nobody cares to understand.