The following changes are in progress:

• An overview of these changes and how downstream code should be updated for the transition guide.
• The flags are still semi-public, the need to move. This means also making them usigned and adding the hack to at least unpickle old pickles with the "negative" flag value. (Follow up to API: Introduce PyDataType_FLAGS accessor for public access #25816).
• The metadata, etc. fields are not actually removed yet MAINT,API: Make metadata, c_metadata, fields, and names only exist on old-style dtypes #25802.
• Expose PyArray_Pack MAINT: Expose PyArray_Pack and deal with PyArray_SETITEM #23893
• PyArray_GetArrFuncs needs docs.