I know Disney recently stated that Sofia the First won't ever count as a Disney Princess because she's too young (less than 15).
That means they want the protagonist to have at least a possibility of romance, if not a genuine love interest already.
Just like
Stormlight-san said, Anna & Elsa (from Frozen) were all scheduled to join the lineup in 2014/2015 but it was postponed (permanently?) because Frozen is/was so lucrative on its own that they put off adding the 2 to the Princess lineup for now. I guess when Frozen is no longer super popular on its own, they'll join the other gals.
But, unofficially, they're Princess #12 and #13.
Disney just released 'Elena of Avalor' and it's 'movie' 'Elena & the Secret of Avalor' will be on TV in Oct/Nov 2016. (It's so weird that they released the series 'sequel' BEFORE the actual movie! :laughs:)
It's said Elena is/will be a genuine Disney Princess. She was created in answer to Sofia not being an actual 'Disney Princess', and who had been previously lauded as the first Latina princess. Since they disqualified Sofia, Disney came up with 'Elena' who, quite amazingly, Sofia discovered/released from inside Sofia's amulet and who had been frozen in the amulet (along with her family stuck in a painting) for 41 years.
Now, Disney is saying that Elena is the first Latina Disney Princess (she's 16 yrs old, and has a love interest---sort of).
So, it seems it doesn't have to be a 'theatre' movie to qualify as 'Princess', since Elena of Avalor is a made for tv movie and tv series.
Mulan isn't a princess at all---by birth or marriage, but they want an Asian 'princess' so she's added. (Though they practically ignore both Pocahontas and Mulan in most of the merchandising!) I was flustered by this so I did some research and 'Shang Li' (Mulan's 'guy') became a Marquis in China during the Han dynasty, so....at least Mulan was, by marriage, a Marquess.
Better than not being royal at all, but still....She's not really a princess in any way....But I love her and her movie.....
Eilonwy and Kida don't make the 'princess' lineup even though they WERE actual princesses is because they aren't the protagonists of their films. (The Black Cauldron and Atlantis, respectively). Giselle from Enchanted doesn't count because her movie is mostly or at least half 'live action' and a parody of sorts of the animated princess features. So she's out, too. Plus, none of them were super big hits, so that doesn't work in their favor with Disney.
(Exception: Jasmine---she's only the love interest of Aladdin, who is the protagonist. But she's still counted. )In the end, it seems one just has to be old enough to have romantic possibilities, and be the protagonist/star of their [hit] film. ^.~
Also, what's with several of the princesses having names that start 'el---' :
Ella
Elsa
Elena
0-o.....I know Ella is fact from the actual fairytale 'Cinder-Ella' so she's safe. But I think 'Elena' is kind of a jumping on the bandwagon that 'Elsa' was such a phenomenon. Does Disney think kids will associate Elena as Elsa because their names are similar sounding?