A few days ago, some interesting stills of what could be Season 3 spoilers popped up on the web. Of course, this brings about some major speculation. Some of these images are, apparently, labeled with what could be episode numbers- namely 312 and 313. Given that this is a half-season, those would be the season finale episodes.
We do know that Trixie will be returning, though, and there are some vectors of her that have shown up.
As for the season length, it is possible that Hasbro and The Hub have decided to move towards the same format that we have with Futurama. The half-season runs are becoming more popular with networks and studios.
Here are the photos via Equestria Daily: