Sorry my friend but that does not tally with the recent historical record of the EU. There any number of decisions that from a purely rational view seemed to be impossible and directly harmful to the various countries and even to the EU as a whole, (eg: the euro, inviting Greece into the euro, the EU constitution (the voters in France and NL said no, not the pols) the accession of the Eastern bloc countries, soon to include Bulgaria, and Romania etc) but they have all come to fruition or is about to. So, unless the EU implodes which is not totally impossible, Turkey will become a member, as will Croatia. Let me end with another prediction: We know from polls that 80% of the Austrians are against a Turkish entry. They wanted their government to stick up for them. The government failed. I predict that after the next election Jörg Haider will form the new Austrian government.
Turkish membership will require a new treaty. Several EU nations constitutionally mandate a referendum to approve all new treaties. If nothing else puts a stop to all this sound and fury, signify nothing, then the task will fall to the Irish or the Danes..
In my view, for Turkey to join, some way will have to be found so that not a single EU nation votes on approving membership, because I think the voters of every single EU nation will reject Turkey easily.