Put the bratwurst, beer, 1 cup water, the caraway, coriander, mustard seeds, onions and ginger in a medium stockpot. Bring to a simmer over medium heat and cook for 5 minutes. Cover, remove from the heat, and let stand 15 minutes.
Transfer the brats to a bowl. Strain the cooking liquid into another bowl, and discard the solids.
Heat the oil in a large saute pan over medium heat, add the cabbage and toss to coat. Add 1 cup of the strained bratwurst liquid, and cook until softened, stirring frequently, about 15 minutes. Add 2 tablespoons of the honey, the vinegar and some salt and pepper. Toss to coat, and cook another 5 minutes. Transfer to a bowl.
Preheat the grill to high, with direct and indirect heat. Grill the sausages over direct heat until the casings are crisp and golden brown on all sides, about 2 minutes per side. Move the brats to indirect heat, cover the grill, and cook another 5 minutes.
While the brats cook, whisk the mustard, the remaining 2 tablespoons honey, some salt and pepper and a few tablespoons of the bratwurst liquid in a small bowl; the mixture should be syrupy. When the sausage are done, remove them to a platter and brush with the glaze.
Split the hoagie rolls and grill cut-side down until toasted, about 30 seconds. Put a brat in each roll and top with some cabbage, then serve.