Thanks @OldUser and @Gabriel5454 for your replies.
Well my husband is adamant that he's filing MFS this year so I'm backing off on this one. But thank you very much for taking time to respond.
From what I gather,
1. It wouldn't make much difference whether MFJ or MFS (I have no idea how he arrived at that conclusion, but perhaps TurboTax said so)
2. He doesn't want to have to mail anything in (if I read correctly, electing to be treated as a tax resident requires paper filing, or at the minimum mail in the letter of election).
We have a lot on our plate at the moment... So I can't blame the poor man wanting to keep things simple.