Just about every track in the country that allows BL has been using 10.5 as the replacement for 19T and 13.5 as a replacement for stock. In other words, many people already have those systems, ROAR changing that fairly widely accepted format will make things more expensive for those that already have systems. Yes, I know people would just have to buy a new motor, but BL motors aren't cheap. Plus, I've heard of people having issues even being able to gear high enough with a 17.5 in a pan car. Which then all of the sudden means there may be certain cars that will become obsolete in favor of car designs that allow for more pinion, people buying pinions they wouldn't normally use, etc.
It just doesn't seem feasible to find a close match with a stock motor and a brushed motor at this time with what is currently available. Doesn't it seem likely that if 13.5 was allowed to run in stock class that brushed motors would become obsolete (it's already happening), at least for a while... If 17.5 is allowed to run with stock brusless motors will be dumped in favor of a good brushed stock motor. Does ROAR feel comfortable with either of those things happening? It seems to be that weight allowance is the one thing that could help even up the current technology of brushed vs. brushless. It's something that many real racing series use as an equalizer and it's cheap... Increase the weight required for 13.5 and or decrease the weight for 27T. The problem is those weights need some tuime to be researched, I don't see it as something that can get worked out in a couple weeks time.