OPC UA Part 5 defines a KeyValuePair structure for generic usage as follows: https://reference.opcfoundation.org/Core/Part5/v104/docs/12.21#Table165

The only problem with the above structure is QualifiedName Key and most of the use cases need a simple String or TrimmedString since key-values are restricted inside a specific resource context.

LADS specification added their type by changing QualifiedName to String as follows: https://reference.opcfoundation.org/LADS/v100/docs/8.1
ISA 95 Job Control added something similar as follows: https://reference.opcfoundation.org/ISA95JOBCONTROL/v100/docs/6.3.7

OPC UA 40450-1 for Joining Systems NEEDS something similar to LADS where the Key is of String or TrimmedString.

Summary:
It might be a good extension to add a new KeyValuePair in the Base Specifications so that other companion specifications DOES NOT duplicate it.