It would achieve a lot more than just that It would that would see the UK, as a whole, remaining aligned with the CU until the EU says we can go. Effectively remaining in the EU without legitimate route out unless we are freed by our EU masters. As such it is one major part of the draft plan that can not be accepted, and would be a betrayal of the UK. Plus, why would the EU want to negotiate further if the inevitable default position, if they do nothing, is we stay put ? No incentive for them at all to do anything.