EPCU is a collective of the euro pony cons. We share information and knowledge with each other to help improve our events and help each other out.
Full Membership of the EPCU requires various prerequisites, including insurance, evidence of success, and so on.
These requirements give an event a stable foundation that help protect it from collapse, and ensure that should the unforeseen occur, people can be properly compensated.
It lets VIPs and other guests know that they can pledge their time and effort without fear of getting stranded in the middle of nowhere with no event to support them.
TL;DR – The EPCU is specifically designed to prevent a Unicon from happening on our side of the pond.
If you fit the requirements of the EPCU, you're theoretically immune to that kind of disaster, where there were no safety nets, and no damage control.
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Who are the members of the Union? Who represents which convention? The rules state a certain amount of transparency from potential members but the EPCU could use some itself in my opinion.
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http://ponycon.org/members/ - GalaCon, BUCK and BronyDays are the only full members. I don't think people realise that most conventions, despite keeping the same name, change a lot of their staff each year (even the chairman etc) so reps can change fairly often.
What is truly the goal of the Union? to be a mark of quality or simply a way for ponycons to make agreements when to hold a convention, so the cons don't have to compete with eachother to draw in people.
-- Yes - the hope was that the EPCU would be a quality mark so that attendees can trust where to put there money. If the convention has the EPCU mark, it's more likely that it will succeed without financial issues (see the main answer above).
Also since the Crystal Fair has ended over a month ago, is it a member now?
-- CF could now, having run once, apply for full membership, if they were willing to show that they have not gone into debt that would jeopardise a future event. Just because a con takes a year out doesn't void their membership, but we do review membership each year; and if a convention is unlikely to run again then they would most likely leave.