I've made connections in NRT where I exited one plane and boarded the next in less than 10 minutes (including my first time). It is absolutely not necessary to make any special accommodations for anyone who has a 50-minute connection there.

Also note that DL is typically very good about holding outbound flights for delayed inbound connectors at NRT since they know they have a single bank of flights in each direction. I've had inbound flights delayed by hours, causing planned 90-minute connections to completely evaporate. Even with my inbound arriving after my outbound was scheduled to have departed, I had ample time to clear security and walk at a reasonable pace to my connecting flight.