Where else is there to go though for DL and domestic service? DL just added the largest market with no nonstop. SNA has been leaving full or oversold the last few days, so if this flight is profitable, I assume the most logical thing to do would be introduce DTW-SJC. The new SNA service hasn't and won't effect the current LAX service as SJC wouldn't interfere with SFO service.
SMF would than be the largest O&D market from DTW, but DL has tried and failed in the past so it's highly unlikely they'll do it again. In the scenario SJC is added in the next few years, the top 3 markets will be (according to PDEW date and general forecasting); SMF, ELP, TUS with ABQ following in a seasonal 4th place. There's relatively nowhere DL can go after than unless they add a very seasonal, RNO, BOI, BZN which they won't do.
Internationally, AM is bringing MTY back on a codeshare which is promising for additional interior Mexico service like BJX, QRO and GDL. There's no way to get a nonstop to BOM, DEL, BEY because of the regional location of DTW compared to coastal or southern hubs, with the exclusion of YYZ and ORD because they're mega cities. When it comes down to that, AMM 2x weekly perfectly serves that area of the ME, FRA and CDG serve India fairly well. I'd say the major gaps internationally are lower cost access to Latin markets and YYC up in Canada, DL won't do YYC though due to the impact it could take on MSP, and WS is capable of serving it from YQG. Realistically more seasonal Caribbean markets could come online like NK on PUJ and DL adding a weekend SXM and AUA flight.
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