Ireland's foreign minister is pressing to get the December agreement into legal text and signed by next month (HERE). Once this is agreed a hard Brexit becomes less likely if not impossible. To avoid a hard border we have to come up with a magic solution to allow trade between two countries who are not in a customs union or a single market and which does not require physical customs checks. No one has any idea how this might work. If we can't do so, the legal text will commit us to retaining regulatory alignment.
The regulatory alignment is notionally between the north and south of Ireland but since the DUP have demanded there be no border between the North and the rest of the UK it means no border anywhere.
The only practical solution at the moment is for the UK to remain in the single market and the customs union. If this is the conclusion then I think we may as well stay in the EU where at least we have a say.
However, I think the hard Brexiteers are likely to cling to every possible straw and won't accept the opinion of experts. They will dream up all kinds of magic but totally unworkable solutions that will need to be knocked down one by one until they are all gone. It might take some time.
