This appears to have already happened on the "digital side" with stable coins buying Treasury-Issued-Notes rather than FR-issued notes. However, to remove the obligation of US Treasury to pay interest to the FR on "issued FR Notes", the circulating bills must ALL be replaced with "Treasury Notes" with "Federal Reserve" REMOVED from all places on the bill (i.e. it is no longer FR "debt instrument" property, but US Treasury issued currency).
This appears to have already happened on the "digital side" with stable coins buying Treasury-Issued-Notes rather than FR-issued notes. However, to remove the obligation of US Treasury to pay interest to the FR on "issued FR Notes", the circulating bills must ALL be replaced with "Treasury Notes" with "Federal Reserve" REMOVED from all places on the bill (i.e. it is no longer FR "debt instrument" property, but US Treasury issued currency).