The transition from the current state of the EU would be virtually impossible -, and the danger of inheriting the dire democratic credentials of the current system is very great indeed. The current paralysis caused by the EU institutions and the member state's power struggle prevent any meaningful reform or creation of meaningful democratic structures; the only democratically elected body cannot even prevent the monthly Brussells-Strasbourg move that has been going on for decades.
The USE won't be a better democracy than the EU; the EU has a democratic deficit which the USE would likely inherit.