I don't know about null, but wouldn't sum types and pattern matching make the language spefication and the toolchains a lot more complex? Their goal has always been to be simple and have longevity, but I think it's been at the cost of "safety", e.g. being able to just ignore errors, allowing nulls (although that's only for pointer types, value types have sane zero values and should be used as much as possible; some pointer types can handle null values as well), etc.

That said, there are other languages with proper sum-types and pattern matching, if that's what you need; I think it's a bad thing that some people advocate for every language to have every feature from every other language. Take Javascript; someone Decided that it should have classes, but the implementation has never been good (e.g. field access levels) and it's always felt bolted on. Take Scala, which borrowed every feature from every other language ever, and now you can't have two people work on one Scala codebase without them having endless discussions about which flavor or pattern to use.