Yes it would be very good if the On Topic List is expanded. The current list is extremely limited, and would define the most popular tag (Aircraft Design) as off topic.
As also mentioned here.
- Aircraft design
- Weight and Balance
- Structures (related to aircraft)
- Aircraft performance
- Aircraft systems
- Flight dynamics
- Thermodynamics (related to aircraft)
- Stability and control
- Aviation engines
- Aviation history
Benefit of the doubt should go towards inclusion, unless obviously out of place. If an aircraft is involved, is the question not by definition about aviation?