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It made so much sense back then, when mobile apps were not that robust to networks changing, I assumed it's going to get adopted in no time due to how much of a ux improvement it would have been back in the day.
It's incredibly depressing that this gained barely any traction in the last 10 years, and kernel options are appearing just recently, after everyone has wrapped they http calls in multiple retry handlers, and mobile operating systems have abstracted network connectivity to the point where it feels more like you are using zeromq rather than tcp.
PS: I mentored a student for 2 years at GSOC to patch Openwrt with mptcp:
https://blog.freifunk.net/2017/05/29/gsoc-2017-add-mptcp-sup...