You already can, if you at least set up desktop, you can transfer also message history, though you won't have your media older than 45 days. Maybe it can work as a stopgap before they roll out encrypeted backups everywhere
That's a weird and crappy arbitrary limitation when I could move an arbitrary amount of data between the two devices otherwise. It's the worst part of Signal.
On top of that you don't have that limitation on Android. It's like enterprise IT, where you put up restrictions everywhere on files and then people can upload files to their personal one drive.
