Some idea/suggestion :
1. Don't use pool to choose best topic, it's more suitable for most favorable topic and could be abused easily.
2. Allow topics about Mining/Cryptocurrency Legality
If this is not a problem, I would recommend discussion about Bitcoin regarding its technology (perhaps something with scalability).
Scalability isn't easy topic and heated discussion/ideology clash will happen because there are many different perspective. Something easier such as multi-signature and seed/mnemonic would be better.