Combine the 2 cups of hot water and porcini mushrooms in a medium bowl; let it stand until the mushrooms are soft, about 30 minutes. Drain, saving the soaking liquid. Squeeze the mushrooms dry, and then chop coarsely.
Preheat the oven to 325°F. Divide the bread between 2 baking sheets. Bake until it is beginning to brown, about 15 minutes. Cool, and then transfer the bread to a very large bowl.
Melt the butter in heavy Dutch oven over medium-high heat. Add the leeks, shallots, and crimini and shiitake mushrooms and sauté until golden and tender, about 15 minutes. Mix in the celery and porcini; sauté 5 minutes. Transfer the mixture to the bowl with the bread cubes. Mix in the parsley, hazelnuts, thyme and sage. Season with salt and pepper. (Can be made 1 day ahead. Cover and chill porcini soaking liquid and stuffing separately.) Mix the eggs into the stuffing.
To bake the stuffing in a turkey: Fill the main turkey cavity with the stuffing. Combine the broth and 1/2 cup reserved porcini soaking liquid in a large glass measuring cup. Add enough broth mixture to the remaining stuffing to moisten (about 3/4 to 1 cup of the broth mixture, depending on the amount of remaining stuffing). Spoon the remaining stuffing into a buttered baking dish. Cover with buttered foil. Bake the stuffing in the dish alongside the turkey until heated through, about 30 minutes. Uncover and bake until the top is crisp, about 15 minutes.
To bake all the stuffing in the pan: Preheat the oven to 325°F. Butter a 15x10x2" baking dish. Mix 3/4 cup of the reserved porcini soaking liquid and 3/4 cup of broth into the stuffing. Transfer the stuffing to the prepared dish. Cover with buttered foil and bake until heated through, about 1 hour. Uncover and bake until the top is crisp, about 15 minutes.