Technically the EU already is an defence organisation (Lisbon accords), even with a stronger mutual assistance clause than NATO. What is different is that there is no integrated command structure. But that is currently rapidly changing, Germany and the Netherlands already are fully integrated (more than NATO standards are), the Baltics are making great progress.
There is at least a chance
Oh,it was thought through very much by some... Some parts of the SVP are very happy about it...