In regards to an unannounced date, that really shouldn't be blamed for screwing with people's ability to plan vacations.
If they DO open on the 21st, which I think is looking more and more to be the case, that's the first day of summer. They've been saying for a long time that it will be open Summer 2014. So if vacationers make their plans for any time during Summer 2014, the area will be open, and Universal has stuck to their word. If people decide to postpone their trips because they think the opening might be later, that's really on them.
Also, if I remember correctly, there were some people last time around who were upset the Universal had advertised "Opening Spring 2010" and then finally opened on June 18th with only a few days of Spring to spare. This time around, a summer solstice opening may be them saying "When we say open this summer, we mean the entire summer."