I think that's a great idea, simple is usually best. Few good reasons for using pob before specific topics;

1. When people see the tag they'll be like "what the fuck is pob?"
2. It will start creating smaller niches within POB and starts forming a kind of umbrella for the platform
3. Easier to find POB posts within specific categories instead of scanning through #proofofbrain or #hive-150329 (this will be a lot more tedious and posts will be missed as the user count grows)

Great suggestion.