How much can EU enlarge and where will it stop? When will it be "complete"?

Turkey, Iceland, Serbia, FYROM, Kosovo, Moldova, even Georgia and Azerbaijan could one day become part of the EU. Which is not necessarily  a bad thing, but it sure makes you wonder if there's such thing as a "final frontier" for Europe.

There's an ongoing debate for the last couple of years in the European media about the enlargement process. Some parties argue that EU should help the Eastern European countries to join as fast as possible, while others claim that the Union itself needs some time to "digest" and integrate the new members that have joined in 2004 and 2007.

So, as a game of imagination, where would you draw the final frontiers for EU and why?