You have to be careful about what LiPo you're talking about, For the single cell voltage a 3.5 was about the same speed as a 5.5 on 4 cells. A 13.5 (sintered) on single cell voltage is slower than brushed stock 4 cell.
My personal opinion is that they should leave the stock and 19 turn classes as is. If we do anything to the stock and 19 turn classes that might slow them down peoples heads will explode.
For mod, I would like to see the option of 2 cell LiPo with a capacity limit on the pack. Limit to say 3200 mAh or so and let the drivers actually drive again. The cars would be much faster on the straight when you pull it but if you pull it too much you'll dump. It puts all of the strategy and driver skill back into mod. LiPo would get a huge weight break also.