This would push users toward local posts (especially on smaller instances) while still supporting a better distribution of user engagement over the threadiverse. And if you don’t trust that it was implemented correctly – you can simply check it by counting the amounts of posts against your chosen probabilities.
Edit: changed feed name to mixed-feed
Wonderful idea - full support on my part 👍🏻
… The Fediverse can only acquire steady growth if engagement in some of the bigger communities picks up and new users are noticing that there is constantly something going on around here - I’m sceptic that with the natural spread of thematically related smaller communities over the Fediverse, we can make that happen without pushing some incentives for community centralization…