Well, it's far from trivial to introduce such a change if you don't want to throw away 3 decades of code/assumptions. Of course null safety would be very welcome, I'm with you on this.
As for unchecked exceptions, that may be a bit of an "unreasonable ask". The only language that properly solves the problem are languages with effect types, which are an active research area. Every other language have either FP-like error values, or just unchecked exceptions (and there are terrible "solutions" like errno and whatever go does), or most likely both. E.g. Haskell will also throw exceptions, not everything is encoded as a value.
In my opinion both is the most reasonable approach, when you expect an error case, encode it as the return type (e.g. parsing an Integer is expected to fail). But system failures should not go there, exceptions solve it better (stuff like the million kind of connection/file system issues).