some very good points have been posted here, but it sounds mostly like a "which is better thread" then a "should it be allowed thread". first let me say a lathe is like a wife, you don't need to have one, just access to a friends once in while . ok now that i got that outta my system. i don't have a brushless system, and right now i don't want one. ok so now you know where i'm coming from. there isn't and never will be true "stock" racing. i remember when i first started racing and my first "big event" didn't say race because it wasn't much of one. anyway, it was a handout motor race. so i'm thinking great. everyone has the same motor. while the label was the same the motors were different. the first thing the "fast" guys did was pull the brushes out, cut the comm, install different brushes, plus side and neg side, different springs. blah blah blah, well so much for a "stock" hand out motor. how long do you think it will take if the BL motors are made the "stock" motor of choice, before someone figures out that if you add a (insert some fancy electronic word here) into the system or open the speed control and change something you will get more torque or rpm. even when in the "stock" profile.
about as close as your gonna come to a stock racing class is the tamiya closed end bell class. but as we all know they too can be messed with.
whether or not the BL system is better or has or doesn't have a "clear" advantage is besides the point. it is a different type of motor then what is currently being used and considered stock. there for it gets its own class, if not enough cars for a class then they run with everyone else, just not counted, or scored seperate.