Compared to other countries already in the EU I don't see that as a huge problem, the Copenhagen criteria could be met. But regardless, it would always be a slow process, first a referendum, then a (heavily contested) formal secession from the Union, then a period to get their house in order and apply for formal EU membership which would then take another two to three years to hash out. I don't see this happening on a total timescale less than five years.
And then there are still the questions of internal borders, Schengen and the Euro.