Three duh's from the article:
Trust models users and networks have fostered with Internet providers are also changed—and in some cases broken. Contrary to that, providers will no longer be able to sniff traffic—under court order for example—unless they work hand in hand with other providers handling split traffic sessions.
They lost me at "Trust models users
“Technology like MPTCP makes it much harder for surveillance states,” Pearce said. “If I split traffic across my cell provider and an ISP I may not trust, in order for a surveillance state to snoop they have to collaborate with all these parties. It’s a much harder proposition.”
Who cares? And if you really care enough, and you are a suveilance state, you can sniff from the soruce, or a common route in between in which all the data flows. Will you have to spend a little extra CPU and Memmory to piece together the full stream? yeah, duh.
Finally, Pearce said, there will be ambiguity for firewalls about what incoming and outgoing traffic looks like. She said that MPTCP enables endpoints to tell servers there are other addresses to which the server may connect, but the firewall may not necessarily interpret that as an outgoing connection.
And not very hard to fix for the firewall vendors. Will you have to patch your FW? Probably. Is that a problem? No, duh.