I think it depends on the "local" CAA.
In DK you need a DME to have a plane IFR certified, and it was not until 6 month ago that you also required an ADF to have it IFR certified.
So all cirrus a/c that wants to fly IFR have a DME fittet regardless of the RNP of the GPS.
It is still a requirement that a plane certified for IFR schoolflight must have ADF.