AFAIK Jason does use wireguard for himself now, but is cautious to recommend that to everyone.
The last submission to the linux kernel is here: http://lkml.iu.edu/hypermail/linux/kernel/1808.3/00619.html
While merging wireguard should not be a problem, its own crypto library called 'zinc' has bigger open points of discussion.
For me this means he's appropriately cautious for working in security-minded applications like this. A lot of VPN providers would probably release something like an alpha release.