I’m also interested in the current progress on transparent materials. Through lots of trial and error, I was able to get something that looks pretty close to a smoky glass for these crystal things. Good transparency, no z-order problems, and even some nice screen-space reflections are showing up.
The only problem I currently have is that the transparent material ignores DOF blur. Maybe hard to tell in this image, but the crystals through that hole on the left should be heavily DOF blurred like everything else down there:
http://lvl17.com/transparent_material_dof.png
Edit: Forgot to mention that this is 4.8, I haven’t gotten around to trying it in 4.9 yet, but didn’t see anything in the release notes regarding transparency.