Yes, therefore it is not required (by this I mean one can be within the EU without being in the Eurozone, whatever the treaty details) – just like Sweden contin

Yes, therefore it is not required (by this I mean one can be within the EU without being in the Eurozone, whatever the treaty details) – just like Sweden continues to be productively within the union while retaining its own currency. The customisable membership (and again, certain core principles cannot be customised of course) is a strength of the EU.