It's been a long dry spell since Rick and Morty's season 2 ended back in October of '15 with poor Rick being thrown into prison on charges of having committed "everything". Fortunately for us, it seems that things are coming together with series writer Mike McMahan having tweeted that they're back in the recording studio.
— Mike McMahan (@MikeMcMahanTM) February 18, 2016
So granted, that's only a few days ago, but they've decided to kick fans a bone for Presidents Day, the entirety of the opening scene. That said we still don't have any solid leads on when the next season will actually see the light of day, but that they're in the studio is a good sign that it won't be too much longer.
Update: Adult Swim Australia has realized that there was something wrong with their editing software. Which means that their temporal plugin wasn't working quite right. Since if they just started recording voices two days ago, if that plugin isn't working there'd be no way to import audio from the future. They posted a follow-up apology while they have a call out to Dr. Who to help fix the software:
Well played Adult Swim, well played.