I came up with a rough concept for a handheld kerbal controller and doodled it. The central buttons and their placement are easily up in the air but my strongest thought was
Custom Controllers for Kerbal Space Program
Gamepad Boat Minecraft Mods - CurseForge
PlayStation Blog - Kerbal Space Program Enhanced Edition Launches January 16 on PS4 - Announcements - Kerbal Space Program Forums
Wirless GamePad not working. :: Kerbal Space Program General Discussions
KerbalController: a Custom Control Panel for Rocket Game Kerbal Space Program : 11 Steps (with Pictures) - Instructables
This Kerbal Space Program controller looks like something from old school mission control - Polygon