I don't think the Eurozone will expand in the near future, if at all. However, I do think the EU has always seen the accession of the Eastern European countries as a long game. Initially, although they had to make many economic changes in order to fulfill the acquis communautaires, their economies were evidently much weaker than those of Germany, France, Benelux etc. The EU, for obvious reasons, wants stability, prosperity and peace across as wide an area as possible. Over the years, the Eastern members should strengthen their economies, as for example was seen in Spain, Portugal, Ireland. While these countries have had their storms to weather, structurally they are light years from where they were pre-EU accession.
I think the EU plays a long game and totally after is still strongly influenced by the fundamental principles that arose from the wars of the last century. I sometimes think that UK governments don't fully realise how deep the scars run, particularly in Germany, and how much the fear of conflict influences policy.
I also think Turkish accession is never going to happen, especially as they have lost their strongest advocate (the UK).