Guillaume,
   Don't see why not, sounds like the right place for it? I rebuilt a 6 kernel some while back for work that had MP-TCP and F-RTO in it along with some twiddling of initRTO as well, those other two are in mainstream now and the MP-TCP patch must have been fairly simple if I managed to work it in. Shout if you need any help, I've got some doco somewhere.

 
Message: 19
Date: Sun, 15 Jun 2014 13:54:29 +0200
From: Guillaume Derval <guillaume.derval@student.uclouvain.be>
Subject: [CentOS-devel] Multipath-TCP in the centosplus kernel?
To: centos-devel@centos.org
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        <A8BF2232-7620-433F-82D0-C74FBEE5597B@student.uclouvain.be>
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Hello everyone,

I am thinking about building custom kernels for CentOS-7 with a support for Multipath-TCP (http://multipath-tcp.org/), and I am wondering if a such heavy modification should have its place in the centosplus kernel?

Modified kernel sources are available at https://github.com/multipath-tcp/mptcp and equivalent patches are there: http://multipath-tcp.org/patches/.

Best regards,
Guillaume Derval.

--
Regards,
   Phil