The rare fairies are not related to the new movie...
2008 Pixie Hollow opened with: Tink, Rosetta, Fawn, SIlvermist, Iridessa
Shortly after the location opened, some fairies became more common whereas others started to become harder to find.
2009 Terrence is introduced, in tandem with the "fall" seasoned movie (other fairies still in random rotation but Silvermist & Iridessa started to fade).
2010 Vidia is introduced, in tandem with the "summer" seasoned movie
2011 Pixie Hollow closes so Tink/Terrence, Rosetta/Vidia are moved to Epcot. Timing correlated with F&G so they use the flower area as a set location. F&G ends in May, but fairies stayed at Epcot for a bit longer until the Nook opens...
2011 Nook opens with Tink & rotating/random friends that traveled from Epcot. Nook space is very different so the other fairies (Fawn, Silvermist, Iridessa) essentially become extinct from regular meet and greets.
2012 Peri is introduced, in tandem with the "winter" seasoned movie and this officially kicks off the seasonal rotation with Terrence in fall, Vidia in summer, and Rosetta in spring. Even with the rotation is swing, if a friend is unavailable another would fill in.
2013 brings us Fairy Week for Limited Time Magic, but with such a gap in appearances from Fawn, Silvermist, and Iridessa - they pop up at Epcot to brush up their human communication skills.
Okay - so no new information there - why the sudden rare pop ups now?
If you do a search for Tinker Bell news (Kennythepirate) you'll see that rumor has it the fairy friends are flying away permanently (not confirmed by Disney). It sure is nice that these fairies are making touch base appearances before they all go away. Terrence, Vidia, Fawn and Silvermist have all been in the Nook a handful of times (each) over the last week or so and will likely continue to do so until a move happens. Iridessa may also appear, she just hasn't yet. Rosetta is still the spring fairy and will be there the majority of the time with any other appearances truly random.
So when does the Pirate Fairy move into rotation? She's not. The fairy franchise has been turned off and there will not be any new character for the next movie release.