Also, I really like this idea, but I think I prefer a smoother, slightly slower damage progression. Personally, I'd go like this:
...d4, d6, d8, d10, 2d6, 2d8, 2d10 (or 3d6), 4d6, 5d6, 6d6...
which corresponds to an average damage of 2.5, 3.5, 4.5, 5.5, 7, 9, 11, 14, 17.5, 21...