Toolkit vendors can add such flags as a convenience to programmers.

A toolkit vendor can add such flags as a convenience for programmers for known namespaces. But a toolkit vendor cannot add these flags for unknown namespaces. For unknown namespaces you only know the DataType (e.g. UInt8) but you do not know the meaning of each bit.
Currently there is no way to describe bitfields in the information model. The information about the bitfields has to be provided in addition to the nodeset. It would be very helpful to provide this information within the nodeset.
Using the OptionSetType is not an option, since it cannot be used for method arguments or as a field of a structure.

Another proposal: Add a ReferenceType "DefinesFlags". You can add a subtype of a numeric DataType (e.g. UInt8) and add the reference to the Enumeration that describes the flags.

This issue came up in the BACnet working group.

Thomas just came up with an example from the OPC UA specification. We use bit masks in OPC UA in different places but do not have a way at the moment to expose the information in a machine readable format.

Matthias Damm will provide a proposal based on the needs of the BACnet w.g.

A proposal will be posted in the meetings folder for F2F San Ramon
IEC 62541-3 - Address Space Model [Pre-CDV] 1.03.03_MD.doc

See changes to table 11 - new property OptionSetValues
See new data type in chapter 8.41 OptionSet

Agreed to changes in Carros meeting.