Here is what is targeted for future versions of xonsh. Any one wishing to tackle any of these or add their own is encouraged to do so!
One of the more genius ideas I first encountered from fish is the idea that man pages can be used to supply matches to tab-completion. In principle this is not that hard. First, we just need to use man2html and then parse the html.
Moving to urwid would allow for a whole new depth of user interaction. There could be syntax highlighting as you type, a real interface for environment variables, and so on. The command prompt is only the start!
Having an Ixonsh notebook would be approximately the best thing ever. It is known.
A true interface to pygments is highly desirable.