Daffy, far as I'm aware, they are required by their accession treaties to joint the euro.
But I do take your point into consdieration.
As of 2007, 11 new EU member states had a currency other than the euro; however, all of these countries are required by their Accession Treaties to join the euro. Some of the following countries have already joined the European Exchange Rate Mechanism, ERM II. They and the others have set themselves the goal of joining the euro (EMU III) as follows:
Personally, I think Poland will the the last of the A10 countries to join. The economy is too weak, big country, lots of people. I would guess 2017, although other economically better countries will join sooner - slovakia, czech