I'd also like to see the details, it seems to be a difficult undertaking but something the EU really needs. As an example, when I incorporate a company outside of Portugal then the tax authority can classify it as a CFC (controlled foreign company) and tax it very high, and it can lead to double taxation. AFAIK, the rules are quite complex. A EU-wide registry should prevent that, but that might require a EU-wide harmonization of 27 tax systems (plus potential associated countries like Switzerland and the UK).