one model for how it's going to work out is the US experience of stronger economic integration with China over the last 30 years. the EU should simply study in great detail the pros/cons of that history.
the analogy seems useful:
* China has the more united and disciplined central government, while the US had a more federalized, decentralized government, approximately like the EU.
* China has based its economic growth on exports, which is far less true of the US (and EU excluding Germany)
* China does not guarantee many (or any) economic rights to outsiders within its boundaries, whereas the US does. similarly the EU grants relatively strong rights, including government financial assistance and medical care, to outsiders within its boundaries
the simplest prediction is that it will turn out roughly the same way as it has for the US, and Germany, the EU zone's current main exporter, has the most to lose.