I'd like to see another planet that could support life. Maybe a small asteroid with an eccentric, elliptical orbit around Kerbol. It could come close to Kerbal once in the orbit, maybe it could be visible from The Mun or Minmus. It could be a Kerbal version of Cruithne. It'd look very lush in some places, with grass and lakes, but still rocky beyond those points. It'd give you something harder to aim for after you've been to Laythe.