Make the cornbread: Preheat the oven to 425˚ F and oil a 9-by-13-inch baking dish. Combine the cornmeal, flour, sugar, baking powder and fine salt in a large bowl. Stir in the eggs, milk and vegetable oil until combined. Pour the batter into the pan and bake until a toothpick inserted into the center comes out clean, about 20 minutes. Transfer to a rack and let cool, then cut into 1- to 2-inch cubes. Spread out on a baking sheet and let dry out at room temperature overnight.
Make the stuffing: Melt 4 tablespoons butter in a large skillet over medium-high heat. Add the chorizo and cook, breaking it up with a wooden spoon, until browned and cooked through, about 6 minutes. Transfer to a small bowl with a slotted spoon. Add the onion, celery, bell pepper and poblano to the skillet and cook, stirring, until tender, about 8 minutes. Add the garlic, chili powder, sage, oregano and 1 teaspoon each kosher salt and pepper and cook, stirring, 2 more minutes. Remove from the heat and let cool to room temperature.
Preheat the oven to 350˚ F and butter a 9-by-13-inch or other 3-quart baking dish. Whisk the eggs and 4 cups chicken broth in a large bowl. Add the cubed cornbread (about 12 cups) and the cooled chorizo mixture and toss to coat. (If the cornbread seems dry, add up to 1 more cup broth.) Transfer to the baking dish, dot with the remaining 2 tablespoons butter and cover loosely with foil. Bake 30 minutes, then uncover, top with the pepitas and continue baking, uncovered, until the top is golden and crisp, 30 to 35 more minutes. Top with cilantro before serving.