I would love to be able to make groups for different crafts and be able to filter through the groups (and not through the craft type). with collapsible menus and so on.
For example:
+ Group: Comm sat [option A: display this group only, option B: hide this group]
| - Kerbin comsat 1
| - Kerbin comsat 2
| - Kerbin comsat 3
+ Group: Mun related [option A: display this group only, option B: hide this group]
| - Mun Comsat
| - Mun rover
| - Mun fuel station
The craft list in career mode gets annoyingly long.