The problem with Turkey allowing a state, or a pseudo state for the Kurds, next to their border, is perhaps not the immediate time. Traditionally Kurdistan, in territory, was composed of areas that now belong to Iran, Iraq, and Turkey.
That is why the 3 countries are in agreement in not allowing the Kurds to have an independent state. They just dont want to lose any territory. If one of the countries, Iraq in this case, allowed such a thing, the other 2 would feel compelled to intervene. Because, even if right now the kurds might settle for the Iraqi part of Kurdistan, in a few years time they might claim, as they always have, the other "lost" parts of Kurdistan, in Iran and in Turkey.
Besides, as was already posted, there is a lot of bad blood between Turkey, specifically the Turkish military, and the PPK, and i don´t see them allowing that to happen.
The current situation, with a Northern Iraqui territory controlled by Kurds, in Autonomy, wich are acting as a de facto Nation, might serve everyone´s interests, even the Turkish, as it allows the pressure from the PPK to dwindle, as they concentrate on their territory in Iraq, cooling things in Turkey and Iran. Wether this will stay like this for a long time, is anybodys guess...
Another note: Turkey needs to make a few adjustments to enter EU, but they aren´t going to sacrifice everything just to get in. Just look at whats hapening because of Cyprus, and thats a small issue compared to Kurdistan.
.pt