As per my knowledge cell matching is done right at the battery manufacturing stage and if done properly then there would not be any need of such a balancing system at the operational level. However there is no harm but only advantage in employing such BMS for every battery stack in an EV.
This article describes clearly the real life problem of the multiple batteries connected. The replacement cost of these batteriies are high there is a good scope for R&D in this area to improve the battery life by employing intelligent chage discharge circuits.
Replay available now: A handful of emerging network technologies are competing to be the preferred wide-area connection for the Internet of Things. All claim lower costs and power use than cellular but none have wide deployment yet. Listen in as proponents of leading contenders make their case to be the metro or national IoT network of the future. Rick Merritt, EE Times Silicon Valley Bureau Chief, moderators this discussion. Join in and ask his guests questions.