I fully believe it would be amazing if he ended up parabatai with Branwell Fairchild and marry Alice Fairchild. The dramatic irony of the twins finally being the Fairchilds to lock a Carstairs down... only took two tries.
The jokes that would enable would be gold. I already found it hilarious that bith Fairchild brothers fumbled a Carstairs but this would sweeten it so much. The meme potential. It would be glorious.