Final/Readonly Support for Fields / Instance Variables
This sort of relates to https://bugs.ruby-lang.org/issues/11911
C# through 'readonly' and Java through 'final' variables/fields allow me to only allow assigning a field in the initializer. It might be nice to embrace some controlled mutation by having this feature in Ruby. Sometimes its tempting in other methods to reassign a field but you really want to control that from the initializer.
Freezing targets a different problem by controlling what I can mutate within that field's object. The two can compliment each other but I see them as each solving a different problem. I know it's possible to freeze an entire instance of a class and not allow reassigning the field that way, but then I'm in an all or none situation where I can't have controlled mutation.