/r/EthTrader tried this with Donuts a while ago and it led to a community split to /r/EthFinance from all of the drama. Adding a monetary reward for comments and posts really skews the incentives of the community members who choose to participate. When you tie things like this to governance (your coins affect your vote weight on the polls) it really creates a perverse incentive for commercial products to come in and create astroturfing content to farm coins.
I think this is a neat experiment and it will be fun to watch what happens but I'm skeptical that this moves the subreddits in a positive direction.