Mixed views coming from the EU regards a rejoin:
Michelle Barnier indicated that the UK could rejoin with the same opt outs as before.
Poland says the opposite.
Jean Claude Juncker has said that the UK will never join the EU in his lifetime. Reasons he gave were:
The EU is wounded by UK decision to leave. Odd statement to make as every EU member passed article 50 in 2009..
UK closeness to the US is not liked by the EU. US is not popular in the EU. For me, that’s the EU being irritated by the fact that the US imposed higher tariffs on the EU compared to the UK. It shatters the idea that:
Bigger blocs = bigger muscle in negotiations
Your version of join is what, Iceland, Norway and Switzerland did. They trade with the EU, but retained their currency and don’t allow free movement. They are also part of the Schengen zone.
UK can’t be part of Schengen as it is a form of border control which wound contravene the Good Friday Agreement.