Fresh sour cherries are available seasonally at farmers' markets.
Bring cherries, sugar, wine, lemon juice, and salt to a gentle simmer over medium-low heat, stirring to dissolve sugar. Cook for 4 minutes. Using a slotted spoon, transfer cherries to a bowl. Raise heat to medium-high, and cook until mixture is syrupy, about 5 minutes. Let cool completely. Return cherries to syrup. (Cherries in syrup can be refrigerated in an airtight container for up to 1 month.)
Fill 8 glasses with ice. Pour 2 tablespoons gin and 2 tablespoons syrup into each glass, and add 5 cherries. Divide seltzer among glasses (1/4 cup plus 2 tablespoons each). Garnish with fresh cherries and lemon zest strips, if desired. Serve immediately.