I highly doubt that Clegg‘s opinion - that the EU needs fundamental reform to make accession palatable - is wide-spread amongst those who favour accession.

Maybe not but I suspect Clegg’s opinion - that free movement is a bad thing and they expect the EU to drop it if the UK is to get closer - is widely held amongst British elites.

Indeed. Free movement and the euro are seen by British political elites, even the pro-Rejoin ones, as terrible things that the UK will need some concessions to be able to accept. A reflection of how the EU debate has moved on since 2016, while the British debate has remained frozen in time.

And no one is going to agree coproduction unless they can be assured that the cross border staffing can be executed without having to wait on the Home Office.