Another idea that could apply to Inferno, Plan 9 or both would be a library for native SVG support. Many (all?) of the primatives in draw map to SVG primitives so this should be relatively straightforward and open up nice GUI alternatives for both Plan 9 and Inferno.

Milestones would be based off of particular primitives with stretch milestones including support for various types of advanced fills, and more complicated manipulation of the SVG objects (transformations, rotations, etc.). A simple viewer would be necessary to facilitate acceptance of the milestones.

A far stretch would be an SVG editor.

This would be a great project for someone to learn about Plan 9 graphics.