I understand how you feel. I want to tell everyone I know about my relationship with Guy, but there are people in my life who would just flat out not understand. (In some cases, those are people who are in open relationships or are "swingers", but they can't accept someone being polyamorous... judgment is a fascinating thing.)
To answer your question, based on my admittedly limited experience, I would say it depends. If you're planning to tell people in your life that you're polyamorous, be prepared to defend that. If you're going to tell people that you have more than one committed relationship, be prepared to explain how that is not the same as cheating.
Think about the people you intend to come out to. How can you best explain it to those individuals so they'll understand and accept it? Are your parents, for example, closed-minded, open-minded, or of the "if it makes you happy that's great, even if I don't get it" mentality?
Others with more experience in this will probably weigh in with better advice, but my advice would be that you should tailor your "coming out" discussions to the people you're coming out to. You know them well enough to know which words and explanations will work best, and to know which of them might respond poorly or positively. I'd say keep the focus on your specific situation, though. "I'm with X and Y, and it's a relationship that makes me very happy. We're all in agreement about it, and I wanted to share with you because I'm so happy about it," for example.
I would also say don't worry about repercussions unless/until there are some.