I didn't realize Iain has a rocky surface !! Want to check :D
Ilve, Novus, Orus, Hetoo, Aquel all look fun to visit - and escape..
"There will be such celestials in 0.8."
I'm looking forward to a high-gravity rocky planet that's possible to land on, but near impossible to escape. Like Eve, but much bigger (or more dense). This planet will be scary (and confuse) for anyone to try to escape. Also like EVE, you need to reduce the Delta V a LOT or burn up on re-entry. Duna is too easy for example.
EDIT: I guess "Ilve" is the largest inhabitable planet. But still a lot less mass than than what I'm describing.
A Jupiter-mass and Neptune size (or even smaller) is what I was thinking of to confuse, scare the pilot, and require huge deltaV to avoid burning up in the thick atmosphere - before doing a parachute free soft landing. I thought making such a planet is just finding a similar rocky planet and change some parameters of mass and size (I may be wrong).
There is also lots of simple alien life in the Kerbal Star Systems. So I hope new science parts are made for finding alien life. Finding alien life will be the discovery of the millennium.
Just offering ideas.
This image below looks like there is life on other planets! That will be an awesome mission to find life as we know it on other planets based on possible habitable planets. Take home a small living sample. Some other planets may have fossil records but no current life.
Another idea is a Kerbin size planet with Jool size mass - an extremely challenging place to takeoff and land with an atmosphere as thick as water near the surface - also fairly easy to implement I guess.