I would also like nominal types in TypeScript, but one issue is that it might open a can of worms that is antithetical to one of TypeScript’s main design goals:

I would also like nominal types in TypeScript, but one issue is that it might open a can of worms that is antithetical to one of TypeScript’s main design goals: that a change in the typing of a program should not be able to modify behavior. If you add nominal types, some people might expect them to be boxed, and thus be able to reflect on types at runtime. So I assume that TypeScript maintainers have made a design decision that users should have to “self-box” nominal types.