Here is something to consider
Horizon distriubutes A123 (26650 sized cells). I would assume it is because they plan on using this cell size in future. Maybe they plan on making RTR's26650 compatible so they can sell more batteries and make more money. They are a business, so why would want to carry a product that does not make money?
First it will be Traxxas, then Losi and then other car makers will be making 26650 compatible cars and trucks so bashers can take their VXL equipped rustler down the street for a 70mph speed run.
http://www.horizonhobby.com/Products...odID=AQR400063