This probably applies specifically to tracing but the attribute specification is under the common directory.

What are you trying to achieve?

It's my opinion that it would be beneficial if attributes could be "inheritable" meaning that any such attributes applied to a parent span would be reflected on any child spans of that parent span. This would be helpful in those use cases where you are tracing multiple spans over the duration of a request and you want to reflect a common attribute, such as a user ID, on every span recorded during that trace.

There is some overlap between this suggestion and with baggage, but baggage isn't necessarily associated with the current trace and I don't believe there is a part of the specification which suggests which baggage should or shouldn't be propagated between services.