Warm the tortillas. Preheat an oven to 350°F / 175°C, then stack tortillas and wrap in aluminum foil. Place directly on the oven rack and warm for about 7-10 minutes. Alternatively, you can char the tortillas over a stove top flame or wrap them in a damp paper towel and heat in a microwave in 30-second increments until warm. Place two warmed tortillas on each plate.
Whisk the eggs. Combine eggs, 2 Tbsp heavy cream, 3 Tbsp chives, 1 tsp Kosher salt, and ¼ tsp black pepper in a mixing bowl, then whisk to combine.
Sauté the onion. Heat a large nonstick skillet over medium-high heat, then add 1 Tbsp butter or neutral oil. Add the diced red onion and cook until softened, stirring occasionally, about 3 minutes. Lower the heat to medium, no higher.
Cook the eggs. Add eggs and cook, stirring often, until small curdles form. Adjust and lower heat as needed so eggs do not brown or cook too quickly.
Stir in remaining ingredients. When the eggs are just slightly runny, add 6 Tbsp cubed cream cheese and ½ cup smoked salmon. Continue cooking until eggs are no longer runny, stirring often, then immediately remove from heat.
Assemble, then serve. Divide scrambled eggs evenly between warm flour tortillas, then top with additional chives and diced red onion, if wanted. Serve immediately with lime wedges.