Here is another interesting idea that could help making the process of adding new rules easier. A simulated / or even spawn command.
This command should not work like summon does, more like a forced random spawn. I've no idea if this is possible but it would be helpful!

/ctrlsim ENTITY x y z
possible console/chat output:

• spawn valid on rule x (5)
• spawn invalid --> no possible spawn rule / no spawn rule