I think it's a very characterful conversion and I like the reasoning behind it. Modeling-wise, I might mix up the colors a bit and do some spots of different-colored rats in each "pile" to break them up a bit, but I can see why that might be more time-consuming than it's worth. Looks like you used a wash to delineate the different bodies and it worked pretty well, I'd say!
And anyone who has tried to hit a rat with a shoe can attest to movement 9!
I'd like to see the rest of your army! I think a gigantic rat swarm of an army would look great on the tabletop, especially against a Skaven army, haha. Keep thinking outside the box!