Originally Posted by
3Cforme
The DL M class requirement goes back more than 10 years... as did the NW Y/B (sometimes M) requirement for mileage upgrades. I don't expect a change in philosophy. Parties seeking Business cabin rides on fares (U.S. origin) less than $2000 need to find a new airline as the OP has done.
NW has some reasonable M fares a few years back. They also had real SWUs that you could use on any fare.