[eclat]

EEA applicability might be less obvious than you imply however.

[graemep]

The integrated taxes would be a very big step for the EEA, so would common company law and governance for these entities.

That said I think the headline proposal (single entity type and single registrar) is not important. The UK and (AFAIK) the US have few practical difficulties with multiple registrars and variations between jurisdictions.