Sounds fun. One thought/suggestion is that it could be made more generic, to basically allow a game to be created out of any predictable event. (Who will win an election, etc.)
I think the main argument against it is that it uses rewards out of the reward pool, but as you stated - if that is what the community is voting on, then it is the community's decision.
If the community decides at a later date that we no longer want to be using the rewards pool for this activity (or at least less of it) - then we (i.e. the whales) would just need to stop voting for those types of posts. It is the type of thing that we can always stop supporting in the future if we decide to.