Anyone know when we can expect to be able to extend FlyNow or Standby on DL flights when ticketed on an NW itinerary?

In LAS I asked about 'standby' options to route via SLC on DL rather than MSP on NW (would have saved me 4 hours in travel time), but was told that you can't standby on another carrier. I couldn't help but say "I thought NW was now part of the new DL according to all your inflight announcements", but was told in no uncertain circumstances that if your itinerary is on NW 012 ticket stock then you absolutely cannot change onto a DL flight.

This seems bizarre as you can buy (on 012 stock) on NWA.com a flight operated entirely by DL.

Anyway - anyone know what the ETA is to be able to switch an NW hub itinerary to DL hub itinerary using either FlyNow or Standby?

Cheers.