Any suggestions for a chicken-based main dish for a Passover seder?

This is a dish I have made for years. You can omit the sherry and it will still be delicious. https://food52.com/recipes/3159-baked-israeli-chicken-in-sherried-citrus-juice

Balsamic Braised Chicken is a nice option, and a good way to make plain chicken breasts a little more exciting: http://www.healthline.com/health-recipes/balsamic-braised-chicken

I was thinking braised chicken when I saw your headline because it is rich tasting and less worrisome than roast chicken, when you're juggling the demands of a crowd.
Adjust to make Passover-suitable (e.g. replace bread with matzah, avoid vinegar-packed products) & you're home free: chicken Marbella from silver palate, a chicken braise with fruit from chef Ferran Adria (i forget title, but easily found on web), various Moroccan tagines, especially from Paula Wolfert. You can even make these in advance .

Here's a great recipe. I've used breasts, thighs and drumsticks for a large family Passover gathering and the dish can be made ahead and reheated. www.toriavey.com Search for Braised Lemon Chicken with Dill and Turmeric. Tori's websites has many other wonderful chicken braises as well.