As suggested by Suminda in this answer, I think a weekly or fortnightly topic challenge might be interesting, though I'm not sure how much participation would be generated.
Please read: How do weekly topic challenges work?
pick one of the proposed topics and post a question on meta challenging users to ask questions on that specific subject
This meta question, and this top level meta question from another SE site shows a good example.
Example topic list:
- Parents and children
- Brahmaviharas
- Speech
- Emptiness
- Riddles #1
- Mindfulness
- Nationbuilding
- Life of the Buddha
- Similes #1
- Monastic order and lay people
- Enlightenment
- Impermanence
- Buddhist traditions
- Intention
- Health
- Parables and anecdotes #1
- Happiness
- One sentence teachings
- Daily life
- Five Aggregates
- Similes #2
- History of Buddhism
- Finance, business and economics
- Samatha and jhanas
- Food
- Riddles #2
- Three Poisons
- Humour
- Social discrimination e.g. racism, sexism
- Actions
- Anatta
- Charity
- Time
- Parables and anecdotes #2
- Dependent Origination
- Renunciation
- Desire
- Teacher and student
- Precepts