I would hypothesise now that the UK has left, France’s proposals for a closer integrated EU standing army and two-speed EU are much more likely to go ahead.

Because of that I see a future in 20 years for something like a three-speed EU:

1. Full integration.
2. Free movement of goods and people.
3. Mutual recognition of qualifications and frictionless framework for EU standard goods back and forth across the boarder. With a seat but no voting rights for the discussion of said standards.