I'm not sure if it is going mainstream right away, but C# is trying an interesting solution to that same problem: reversing their default relationship with 'nulls' and adding in optional syntax to flag variables as 'nullable'.

In terms of backwards compatibility the language teams position, IIRC, was that in the cases where you are intentionally using null it's quite easy to find and flag flag the nullable variable, but in all other cases the unexpected nullability can responsibly be removed from apps, making then-unnecessary null checks superfluous.

It's a bold move, but if it works at scale Java might be able to pull the tablecloth out from under the plates too...