The exhausting attempts to squeeze such a heterogeneous functionality into 128 bits gave me the seditious thought of JSONB format as a container for UUID. See https://postgrespro.com/docs/postgresql/13/datatype-json for JSONB format. It is binary and indexable.
Formatting, bit-length change, and Encoding are out of scope for this RFC. Marking off topic and closing to clean up the issue tracker due to little discussion about this one in particular.
The exhausting attempts to squeeze such a heterogeneous functionality into 128 bits gave me the seditious thought of JSONB format as a container for UUID. See https://postgrespro.com/docs/postgresql/13/datatype-json for JSONB format. It is binary and indexable.