According to a recent Twitter post from Dylan Cuthbert, Q Games is working on a PixelJunk 1-4 demo.
Here's the tweet:
"About to go collect an order of MOS burgers for everyone still at Q working on the PixelJunk 1-4 demo"
Cuthbert told Wired back in March that his company was currently at work on PixelJunk 4 and other titles in the series.
Hopefully this means we won't have to wait much longer to take a gander at it.