As mentioned in the roadmap and the cross-platform page, we're working on a cross-platform userspace client, so Mac and Windows users can use it too. It's in the works!
This comment was marked 'dead', but I think it was a useful question (though maybe a little aggressive in its wording):
> So what's the point ? Linux is a niche market. Mac & Windows will be the vast majority of your users and won't enjoy your killer kernel-based feature...
Even when Windows/Mac are the vast majority of clients, each client only needs to process its own traffic. The VPN gateway is more likely the bottleneck, since it needs to process everyone's traffic. There are many organizations that would have no problem running Linux on the VPN gateway and could reap the benefits.
Also, the Linux in-kernel implementation is just the first(?) thing being released. WireGuard is a VPN protocol and its killer feature is good security that's simple enough to implement in 4000 lines of code. This simplicity makes it easier for someone to write a Windows/Mac kernel driver.
