Sounds good, are you suggesting to modify the spec in the meantime for IFC4x, and then in the next IFC5 release, revise the description of IFC GUIDs to a canonical UUID representation of 36 FIXED STRING xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx?
I think this is a very clean and simple solution. This also prevents the issues with the non-standard base64 charset and complexity-adding padding truncation.
In a separate discussion, a clearer definition of the purpose of a NULL GUID can be defined. Maybe we can also decide whether it is worth it to promote a specific UUID version?