It's a project years in the making.

Yes, massive respect for that type of perseverance on long term, important changes.

Seems like a horrible way to work. Why could this not have landed as a large amount of smaller PRs in a more incremental fashion, maybe Java users could have gotten some value out of it earlier.

50% maybe.

There are other projects that depend having it in place, SIMD (vectors), reiffed generics, non nullable types.

Java has a mechanism for Integer and Long objects caching using something that already looks like value object, cached objects can be compared using ==. hashCode of Integer already returns int, the boxed int value. Not much of value is lost.