I've got a few comments to throw in here. I've been out of racing for several years now and getting back into it just for fun. I used to be highly competitive in my area and plan to run mod/19t and no stock. I want to go Lipo b/c it is less hassle. Yeah you still need to balance them and what not. But, you don't need a seperate discharger and extra time to do it. You also don't need to worry as much about whether the cells will still be good after sitting for a couple months.
At first I really liked the single cell idea. As the goal is to slow the cars down across the board. At least that's my understanding. I'm all for giving the up and commers their class back (i.e. stock). If that's the case then why change the motor specs for the classes so that they remain even? Shouldn't the rules just switch on some predetermined date? Say, sometime in July when racing is generally slow. All the rules and classes stay the same except for the battery requirement.
The single cell car has another issue that I see. Gearing! From what I've seen it's pretty tough to find proper gearing as is. Decreasing voltage is going to make it even harder b/c you will have to gear up. That may lead to new rear pod designs to allow for more motor movement. Of course the pod designs are already changing to adapt to brushless motors.
The biggest issue I see with the 2-cell setup is speed. Mainly, how do you slow the cars back down with the voltage increase? I don't really have an answer to that. I'm sure someone makes a motor that would be slow enough though.
The main advantage to the 2 cell setup is overall weight and cost. The smaller motors and speedos don't cost near as much as their big brothers. Smaller motors require smaller batteries which further reduce cost and weight. Less weight means that everything is more durable. This option also greatly increases the motor rpm meaning that these ridiculously high gear ratios can be brought back in check. The smaller motors may need different pods. But, it's something that is already changing so what's it mater if it changes a little or a lot? It's still different and non interchangeable with current/previous designs. And, less weight means less tire wear and lower cost.
I've got the equipment to build my car either way. I'm choosing the 2-cell path. At least for now.