The one & only Golden Rule for addons that is absolutely inviolable and immutable;
Addons Must Not Change Core Code
Other than that, anyone uploading to the addons area, can do as much or as little as they want. Simple code, complex code, Images, Video, Screenshots, a 10 page PDF of usage instructions etc. Or not.
I don't want to police the addons area; perhaps potential users of addons can do that - by asking addon creator for video, more images, screenshots, etc.
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- The merchant facing mantra needs to be "no coding needed".
- The developer mantra needs to be "no core changes".