Sounds rather like a plan to me, PIM. There is absolutely no reason why it shouldn't work. In fact, I'm going to try it with venison, cuz they're a natural match.
Just one comment: Technically, a Shephard''s Pie is always made with lamb. That same technique (i.e., using mashed spuds as a top crust) is generally called a Cottage Pie when other meats are used---except in some locales where, if venison is used, it's called a Deerstalker Pie.
I love sweet potatoes, but dislike the saccarine-sweet concoctions usually made with them; preferring to use them in breads and savory dishes. Here's one of my own:
Sweet Potato Timbales
2 cups mashed cooked sweet potatoes*
1 apple, peeled, cored, and diced fine
1/4 cup apple cider
1/4 tsp nutmeg
1/2 tsp cinnamon
1/4 cup currants
1/3 cup yogurt
1/4 cup orange-ginger syrup
1 egg, beaten
1/4 cup hazelnuts, ground
2 Oranges, cut into segments**
Lightly grease muffin tins with the butter. Dust heavily with the ground hazelnuts. Set aside.
Preheat oven to 375F
Cook apples in cider, witht he nutmeg and cinnamon, until tender (about five minutes). Turn off heat. Mix in currants. Let cool.
Combine the sweet potatoes eith the yogurt, syrup and egg. Mix in the cooled apple mixture. Spoon potato mixture into prepared muffin tins.
Bake until set, about 30-35 minutes. Let rest five minutes and unmold onto a sheet pan.
Top each timbale with a an orange segment or two, sprinkle lightly with sugar, and melt sugar with a torch. Transfer timbales to a serving platter or individual plates and drizzle with more syrup if desired.
* I prefer baking the sweets over other cooking methods.
** Tangerines can be substituted for the oranges
I don't remember where I got the following recipe, but it's another great savory use of sweet potatoes:
Sweet Potato Balls
1 lb sweet potatoes
1 small onion, minced
3/4 tsp grated fresh ginger root
1 egg, beaten
1 tbls butter, softened
2 tbls flour
1 tbls parsley, chopped
2 cups whole wheat bread crumbs
1/4 cup oil
Cook sweet potatoes. Peel and mash them, and combine with all other ingredients except the oil and bread crumbs.
Heat oil in a heavy skillet. Place the bread crumbs in a bowl. Form small balls by dropping a heaping tablespoon of the potato mixture into the crumbs, dredging each ball through the crumbs to coat well.
Fry in batches in the hot oil, rolling them around to brown all sides. When golden brown, drain on paper towels and serve, or keep warm in oven until ready to serve.