Place cream cheese in the bowl of a stand mixer fitted with the paddle attachment. Beat on medium for 1 minute until smooth.
Scrape down the sides of the bowl, add sweetened condensed milk, vanilla, and salt and continue beating until combined and smooth. Scrape this mixture to a large bowl.
Add cream to the stand mixer bowl (no need to clean it out) and using the whisk attachment, whip the cream to stiff peaks, about 3 minutes.
Add a third of the whipped cream to the cream cheese mixture and fold to combine. Add remaining cream and gently fold until completely incorporated. Scrape into a 9×13-inch baking pan and smooth top. Cover and freeze for 2 hours.
Meanwhile, prepare the blueberry sauce. Combine blueberries and sugar with 2 tablespoons of water in a medium saucepan. Place over low heat and cover.
Cook, stirring occasionally, until blueberries are soft and sauce is slightly thickened, about 15 minutes. Let cool completely before stirring in mezcal.
After 2 hours, drop tablespoons full of blueberry sauce on top of ice cream base. Using a skewer swirl the sauce into the ice cream then cover and freeze until completely solid, at least 2 more hours.