For the DUP, if they agree to a border in the Irish sea it ends their entire raison d’etre. That will destroy them permanently, so they will oppose it.
BoJo I feel will get tacit consent from Sturgeon in return for a indyref 2 agreement.
There won’t be a border at the Irish Sea. There will simply be ID checks. If you’re a Brit living in Northern Ireland, no problem. Just bring your ID along. It would not be tough to pick out the Romanians let alone the Arabs and Africans from the natives.