i mean that's pretty much already done via third party and endorsed by the bsky team (i can already follow mastodon users on bsky and bsky users on mastodon);
https://github.com/snarfed/bridgy-fed
(shameless self promotion; my bsky account on my mastodon instance: https://tech.lgbt/@[email protected])
to be fair it was originally not opt in but it was mastodon users who made an issue about it and forced the opt in version
and bsky has multiple algorithms because individual issues can create lists and feeds tailored to their needs.
it also has a straight forward following feed