Looks very interesting. I tried the Windows build, but I can't get it to show any preview image. Tried selecting nodes and double-clicking them -- nothing. Maybe it needs to recompile the shader manually, but I haven't found any GUI command or hotkey for that. Checked the log, but it looks OK, no errors.

UPD: I managed to get it to show the preview: 1) Delete the default nodes (Read Image and Write Image). 2) Create a Checkerboard node. 3) In its Properties, set Size to anything except "As Input".

You can then plug it into filter nodes (e.g. Directional Blur), but the preview is still fickle -- at some point it just disappears and never shows up again until I reset the project.