Whatever ones will keep the UK happy? Maybe let them have their stricter immigration rules that they wanted in 2015? I'm not sure, that's for the EU and UK to figure out. I don't think the EU will budge (nor should they, really) so it's all pointless anyway.
What is the point for the other 26 countries, what concessions the UK offers? I'm not against the idea but in that case I would ask for zero rebate and no access to the service market.