I think Canon is leaving the pancake game to Pentax. Although you're seeing some in Fuji and 4/3rds which makes a lot of sense. I think Sony are idiots for not pursuing physically shorter lenses with all their small mirrorless bodies. Maybe Zeiss refuses. But they're missing an opportunity. But then Zeiss has Voigtlander!
Maybe in Canon M you'll see more pancakes. Maybe. The 20 is a good indicator. I'd bank on the 40 stm being it for full-frame and apsc dslrs though.
But you mention the Voigtlander. I just bought one a month ago, and love it. At a 20mm focal length (I'm talking about full-frame) having autofocus isn't really that big a deal. If you're into wide-angle action, then I think you want both auto-focus AND a zoom for quick response and immediate flexibility. Get a 17-40. But for everything else, manually focussing on a 20mm lens is very safe, and the focus-confirm indicators on my 6D work great for ensuring I'm in focus. Typically, when I switch to the Voigt, I half-press the shutter (every time, I do this!) and nothing happens. Then I remember I need to focus the thing manually. And I'm good from then on. It's not hard at all to do, you just have to do it.