Could someone explain more why this should be a language feature?

My understanding of template strings is they are like f-strings but don't do the interpolation bit. The name binding is there but the values are not formatted into the string yet. So effectively this provides a "hook" into the stringification of the interpolated values, right?

If so, this seems like a very narrow feature to bake into the language... Personally, I haven't had issues with introducing some abstraction like functions or custom types to do custom interpolation.