It sounds like a confusing loophole but one I'm definitely interested in learning more about.
It got closed on the back of the UK v McCarthy ruling in the EU courts, as too many were doing it. EU law was changed for EUs in the UK to, if you are a Brit then you can't be another citizenship for immigration purposes.
Well, if you renounce your British citizenship, then you can move to the UK using your Irish citizenship and exercising your rights to live in the UK.
Think carefully about whether you would mind never having British citizenship again as you might not be allowed this again after you renounced it, especailly if they think you did this to get around UK laws. Being granted British citizenship is discretionary, not a right.
If you give up your British citizenship to bring a non-EU to the UK you would have to exercising treaty rights at all times as a qualified person for him to continue to have a right to reside in the UK, it's not just a case of living in the UK.
EU citizens must either be a worker, jobseeker (limit 6 months), student with private health insurance to pay the NHS and can't have UK benefits, self sufficient who entered with several thousand pounds with private health insurance to pay the NHS and can't have UK benefits. You would also need to keep up to date and comply with all the changes the UK keeps making for EU citizens.
I think the Irish can use the NHS for free if they prove they are residing in the UK even if they aren't working, but if that happened your partner would need private insurance to pay the NHS as he isn't an Irish citizen and you would have a limited time to find a job so that he could continue to have a right to reside in the UK.
The EU permit he would get when he entered the UK only remains valid if the EU citizen remains a qualified person. The end date of that permit doesn't really mean anything as the permit becomes invalid if the EU citizen stops being a qualified person.
If you could manage to be a qualified person continously for 5 years (and the UK need proof that you have) and the UK doesn't vote to leave the EU in 2017, then he would have PR in the UK after 5 years and a year later he could apply for British citizenship. Whether you could receive Brtish citizenship after you had renounced it, would be at the discretion of the Home Secreatary.