This read/write split is also good for documentation/safety, right? Now the type documents that your function isn't doing any writes, which is cool. That's a much less powerful advantage than being able to safely use a read-only replica, but it applies to more people.
Would be good to mention if this causes breaking changes. IIRC from the original PR it shouldn't for anyone but maybe library authors, which people will want to know about.
Blog post explaining some of the thinking behind the upcoming split DB change.