I like the idea. My only concern is the time it would take. RISK is notoriously long, and battles are decided with just one roll of the dice. I can't imagine the length if every battle was settled with a game of Warhammer. Cap it at 5, 6 weeks for sanity's sake.
Perhaps there can be a turn order in resolving territories. Each player adjacent to a territory can choose to join the fight, making or breaking alliances however temporarily.
Each point on a territory could be worth 100 points, with a 500 point minimum.
I feel like with some tweaks, it's possible to get something like this working. Would people be happy playing it? I have no idea.