My Opinion about any changes to Batteries in 1:12
The goal to replacing the powersource if needed to replace with a power source as similar as the one in current use.
I belive the Li-Ion batteries with the Iron-Phosphate chemisty are about as close to a match that be made with current technologies.
This is why I think LiFEPO4 cells are a good replacement.
1.The cells are more durable and safer that NiMH or LiPO.
2. Most electronic in our cars need a 5V powersource, Going to 3.7V would
require a RX battery(Those days are over, Thankyou BEC)
3. Since the only logical choices are LiPO or LiFePO4 in 2S I would rather choose the lesser of the voltages, in this case 6V vs 7.4V
Now to address the motor issues with 1:12
There are 21.5 Motors, Novak has them and Tekin is rumored to be making them. Since ROAR has 21.5 motor classes in Oval, it would seem to be wise to adpot that powerplant also. In oval they run 21.5 with LiPO but restrict the capacity to 3200. The limited capacity lets the votlage drop over the 4min race, but the speeds are still comparable or faster than 4-cell 13.5 oval.
In either case, with a battery change, I am in favor of using a 21.5 Motor if needed for the stock class but would perfer 17.5. With the battery change I would like the rules set a year in advance before the offical switch date. The touring cars are a mess right now because when the packs first came out they were clones for NiMH for fitment. Then some wise-crack decided to make the bricks taller increasing the capacity and performance. So just about any racer who wants to be competitive must but the freaking largest capacity pack and mill and hack on their chassis to fit the battery. More capacity = higher average votlage during a race.
A simple rule for any new battery for 1:12 could be Sub-C formfactor or or total Battery case of 45mm x 23mm x 92mm. This would first limit the possible capacity and second allow the cars of today to be compatible with the batteries of tommorow. Limiting the capacity is a good way of bringing back "battery-management" during a race. Its been years since I dumpped, and I kinda miss "slower is faster" driving.