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
I just called it Explore because its called that in Mastodon. Mixed is also fine.
To include Local, you could also make a slider with two slide-poitns:
Local All Subscribed
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