Transforms and Vectors are still floats. Meaning it’s not yet using double precision for world positions and such. It’s misleading to say that UE5 supports double precision. It doesn’t yet.
The commits in github on the main branch are low level math functions and SIMD vectorization stuff. Given how low level these changes are, work on this feature seems relatively new(but I don’t know for sure). You can’t change your actors to use double precision transforms until your math functions can work in double precision. This feature is going to be a bear to implement throughout the engine I suspect.
I too am very curious what is meant by remove some of the limitations on world size.