A good low calorie alternative to pie crust?

I don’t think anything is worth trying. You could make something low carb, but not really low calorie. Skip the crust, but don’t bake in a pie pan. Bake in individual ramekins and top with a little bit of crumbled cookies when serving to get some crunch. Ginger snaps would be great with pumpkin pie and you don’t need to use much so not a lot of calories.

Pie crust is OMG like one of my favorite things, please don't mess with the crust.

You can still make pie crust using flour and low-calorie margarine--exactly the same way you would make it with butter or lard. Use stick margarine, well-chilled, about 3 tbsp per cup of flour and a little water to hold it together so you can roll it out. Cut in your margarine, add water enough (by the drop--not the cup) to make the dough pliable, and roll into a crust. Bake as usual. 

This might sound weird but what I like is mash potato on the top, no need for milk or butter in the mash, just boil the potatoes, mash them with just a bit of salt and pepper and bake. The result is a bit like the top of cottage pie you just got to get the top of that mash golden brown it will be slightly crispy. One way to ensure that is to run a fork through the mash before it goes in the oven. Butter and milk in the mash ruins the crisp texture plus un needed calories. Try this it really is lovely 

Make a smaller pie.

If you're that worried about calories dont eat pie. 1000 calories is for the ENTIRE crust. Not a single, reasonably sized serving. Microwave some sugarless fruit and crumble a gram cracker on top. Unless you're afraid of fat free gram crackers too

Bake your pie with no crust and make a crumble, almost like a streussel topping and  add that to the top as each slice is cut or it can be added before the pie is baked. 

If you opt to add it as the slices are cut make your crumble then sprinkle it on a sheet pan and bake it in advance, let it cook then break into bits. 

Another option...

Bake without a bottom crust then make a lattice crust for the top. cut the strips thin and lay them over the pie.   Or    make your crust, cut decorative pieces and lay them on the top of the unbaked pie.  For example for a pumpkin pie cut out a pumpkin for the center then leaves around the edge. 

I often bake "pies" in individual ramekins.  If you want a crunchy bit 1 single cookie on the bottom of the ramekin or on the top after it is baked. Or some home made granola would work as your bit of crunch

You could try a graham cracker crust, I guess.

Splenda?   Yuck. 

Unless you are fat and frequently eat dessert, just bake a pie the way you like it.  It isn't going to kill you.

If you're obese, then just roast some pumpkin and eat it.   Dessert is not for you.

Maybe a gram cracker crust, made with Flora / low fat spread?.

To me, all of the manufactured zero calorie sweeteners make food and liquids inedible and not palatable. To me, try to use better ingredients, learn to enjoy less sweet and smaller portions.

Honey and/or real maple syrup instead of sugar

whole wheat flours mixed with graham cracker crumbs in a thinner crust.

If the filling solidifies in baking, buy a spring form pan

Greek yogurt instead of cream, maybe add a whipped egg, 

real vanilla and nutmeg with cinnamon gives a spice flavor that tastes sweet

Search and experiment for recipes.