Hi @theoretical, as you like system design, here's an additional idea:
When Powering Up you can directly upvote and influence the rewards structure with your stake, this incentivizes people to participate and engage with content on the platform. (as it is now on Steem)
But, Powering Up should not directly lead to a full stake-weighted vote for governance purposes (voting for witnesses). How about people would gradually earn witness voting rights over time? For example 1/13 of the total voting rights per week? Maybe even slower? (a proposed idea to mitigate the potential risk of a abrupt hostile takeover)