Squad should add a new turbojet, something in between the turbo ramjet, and the wheesley. Not a panther engine though, just something that will work better at higher altitudes.
The J75 was used on the U-2 spy plane to carry it to the edges of the atmosphere. We should have an engine that is smaller, and capable of doing this with really good fuel efficiency early on in the game, and to provide a way to air launch something from the edges of the atmosphere, or to do some early exploring of Kerbin.