It would strengthen the ties between the EU members if NATO membership was the same as EU membership. So there is merit to that if you want greater European integration. It's why the United States is so integrated because of having a common federal military in addition to the 50 state militaries. On the other hand, if you are a Eurosceptic, then Orban's proposal may be not so great. Also, a bunch of NATO countries would have to get the boot, not just the U.S. Turkey and Canada for example.