I think that San Diego could work. It is 18th largest MSA in America at 3.27mil, just above Denver at an even 3.0 and they are a four sport city. I also see potential for bringing in fans due to the relative sports vacuum created by the NFL leaving.
I guess the biggest question is if you want to go to the 18th largest MSA when you have holes in #5, #6, #10 (Houston, Atlanta, and Phoenix respectively).
I think San Diego is definitely a place the NHL should target, because while you mention three cities with more people... those other markets have NFL and NBA and San Diego does not.
It's the fourth-largest market without an NHL team.
It's the fourth-largest market without an NBA team.
It's the fourth-largest market without an NFL team.
Think of it from the perspective of "fan dollars per person needed to provide league average revenue for all the market's big five teams." That's obviously not how it really works, but it shows you the likelihood of one team being financially successful.
For example, NY and LA have so many people that it's like $60-$75 per person to reach the average revenue to have ONE NFL, MLB, NBA, NHL and MLS team in those cities. For the 11 New York has, it's $146 per person.
So to add an NHL team would be:
$210 - Houston
$221 - Atlanta
$226 - Quebec
$293 - Phoenix
$187 - San Diego
(Again, this isn't like "how it works" because corporate dollars are a massive factor, which is why everyone's gung-ho on Vegas, which is $323 per person for NFL and NHL now, and would be $643 if they get an MLB and NBA team.)
But it does illustrate how the market saturation for sports dollars is real.