It is good to have "Via keep out" routing layers information in EMN file export and in IDX file export. As most of our users need this information while exporting the EMN file for sharing it with ECAD team.
As of now this information is lost when we do the EMN file export and there is no way we can add this information in exported EMN file.
As per the case #14990483 support engineer confirmed "Via keep out" does not support Routing Layers (according to the IDF 3.0 spec). These attributes are ignored because they are not applicable for Via Keep Out.
And IDX also works the same as IDF (.emn). This means the routing layers (TOP/BOTTOM/BOTH/INNER/ALL) and board side (TOP/BOTTOM/BOTH) attributes are not applicable for "Via keep out" as per IDF spec.