In so far as individual european states retain own civil aviation authorities and rules of employment remain a national interest then an eu wide pilot union will never work!
Some EU states promote own national interests while only a few countries open up their pilot job markets to all european nationals. Indeed, in some eu countries, it is impossible to find other non-nationals working their airlines. They used language, licence conversion and any other reason to better own interests. This then means the muscle required to ensure an EU pilot union success is huge let alone deemed to be in place b4 the current incumbent pilots are in employment, i.e occur within next 20 years.
Similarly, the disjointed nature of pilot outlook at own careers will not support an eu-wide union perspective. Pilots are the first to agree to low wage schemes, even undertaking cabin crew tempo conversion training in order to retain own butter. Some even pay-to-fly just to get a foot in the door. As such, this our profession has lost its credibility and marketability for top management within airlines.
Complaints about recruitment agencies abound and yet the pilot is nowhere to be seen running own recruitment agencies. This only strengthens the ideas that pilots need a headmaster figure to manage even own careers. Airlines have supported these views in order to weaken pilot [management] bargaining strength. Small wonder then that pilot salaries have eroded to such levels it no longer is among the most sought after career path for youngsters.
An EU-wide pilot union would need to start at common european wide legislation. This in turn requires a similar but user adopted common mandate of management, employment, terms and conditions, benefits, etc that apply to all eu aoc holders. In the absence of this, only sporadic strikes here and there within the eu will take place with no common agenda or resolution.