I imagine that'll be popular with the people of NI. Essentially what you're saying to NI is if you didn't vote Brexit, it's tough $#@! oh and you need a passport to travel to the U.K. which you're still a part of.
Small price to pay for you not wanting something you didn't vote for. Suck it up cupcake you're out of the EU and you'll like it OK.
You can't divide the UK up like that, what's next, Scots need a passport to travel to England? and do mainland Britons need a passport to travel to NI as they couldn't get back without one and who does those checks? Essentially your goal is to break up the Union isn't it, starting with the isolation of NI.