Preflight testing

Basically, it would be a small window in the designer that will show like a simplified render of what something will do in flight.
You could set it to render the following:
1. Vizzy scripts
2. Robotic part deployment
3. A very simplified 2D version of the ascent, to ensure that the aerodynamics are correct and the TWR will be stable throughout the flight (I hate spending 2 hours on a craft, just to find out that it immediately flips, and then I have to load and reload)