Very cool project. One downside to this approach is that each tcp connection cannot use more than one link's bandwidth. I've been meaning to try this with a multipath VPN to work around that issue but haven't had the time yet.
I tried this[0] and successfully round-robin packets in a single stream. Problem was that the two links had different latencies and Linux has no tolerance for out of order packets. Instead, it would cause a huge number of retransmissions. [0] https://github.com/erjiang/tuntuntun
Interesting, even so was it a net win?
It looks like tuntuntun is pretty basic, my thought was OpenVPN with null encryption over MPTCP. But the combination would obviously have a lot more overhead than that.