"The Minecraft Movie" has been in the rumor mill for a few years. Some people thought it would never happen. Now, Warner Brothers has acquired the rights from Minecraft developer Mojang AB. Warner Brothers plans on making the pixelated game into a live-action film, and Roy Lee, the producer behind "The Lego Movie" (which I never watched) will be working on the project under the production company Vertigo Entertainment.

This (see above) is the tweet by Markus Persson that started all the buzz.
It's a little early for April fools jokes, and Perssons has confirmed that the news is real.

"It would be nice to tell people when it's 100 percent solid rather than to leak it before it's completely final, but our hands were a bit tied and rushed here." - Markus Perssons

I have very mixed feelings about the film, I feel enough people will watch it so that it will be considered a "success", but I would be surprised if it were actually any good. Minecraft is fun to play, not to watch, as evidenced by the thousands of terrible Minecraft Let's Plays on YouTube.