I think JFK-SEA will work. It definitely has the premium demand on both ends, DL should be able to split the market with B6 (whenever they start Mint on that route). It looks like 2 of 4 daily flights on this route will receive D1. From what I hear, 1-2 of the flights on this route are lie flat already so it seems to just be an amenity switch.

JFK-SAN has potential to work, but I worry B6 has already taken the premium passengers. SAN has no legacy carrier with a strong foothold, so passengers are more up for grab (compared to SEA where DL has a strong FF base) and B6 simply has a better product. On the NYC side, many fliers are already B6 customers as well because of their big JFK operation. Also, there is only going to be D1 once per day vs. 2x Mint from B6, so frequency could be an issue.

JFK-LAS is kind of risky. LAS is a very leisure/low cost market, and I only think B6 has a chance of making Mint work because it's priced so low. Does DL really want a fare war on this route for D1?

Also seems like BOS-LAX is getting D1. Like BOS-SFO D1, this seems like a move being done to stop the bleeding B6 is causing at BOS. DL didn't care when the leisure passengers switched, but they are mad the premium ones are going too. This route will probably do well because there should be enough demand to support B6 and DL. However, I think it will not stop passengers from switching allegiances.