So, in anticipation of this reveal Saturday, I looked back on DP and BW prerelease info, and I found BW extremely similar to XY!
In February 2010, Zoroark and Zorua were announced / In February 2013, Sylveon was announced
In that CoroCoro for both, more information was going to be announced in the March issue
In March 2010 and 2013, no new info! Hahaha
This is when it gets creepy: In the beginning of April 2010, the show Pokemon Sunday showed exclusive footage of Black and White before CoroCoro. Serebii even admits himself that it was an unlikely source from his post. (This sounds oddly similar to now, how Pokemon Smash is revealing a new Pokemon with potentially something else...)
Later that month, the starters, cover legendaries, screenshots, and protagonist art were revealed.
Now, since Chespin, Fennekin, Froakie, Yveltal, and Xerneas have already been announced, it differs from BW prerelease information, but I feel like there is some sort of pattern here. Hopefully we get something that ties in with the movie.