With the way things currently are there needs to be room for both. I don't think companies with a major vested interests in brushed motors (springs, arms, cans, brushes) would want to be put under with the BL technology.
Being an average long time racer I have invested time and money into brushed tech. I have everything I need to make and maintain the motors, short of winding and zapping. Would be willing to give up all the maintenance? Sure in a heart beat but it is easier to maintain what I have instead of buying 3 or 4 new systems which would be big money more than I care to spend. I could not just buy one, because I would need a back-up in case something happened. Also usually I don't like to be the 1st one in line when something new comes out. I would rather wait till the tech gets proven, prices drop and classes are available.
If I were new to the hobby, like one of my friends is, I might consider going BL 1st because all my money is not tied up in brushed tech and it is "easier". Although my friend being new to the hobby is a decent driver does not have the finesse in using BL tech on the track, which means more frustration and broken parts.
Another friend who is heavy into BL tech has been able to hold off sponsored drivers in open mod. He is another average longtime racer who got fed-up with brushed tech and switched to BL. BL tech made sense to him because he literally loves to run every day.
If I had to forcast a future to BL tech there needs to be some templates for companies to stick to making "legal" BL systems. I could see 3 levels for BL in cars a beginner, a "19t type" and an "open mod" level. Maybe a new terms needs to be created like BL1, BL2 and BL3 in the spirit of SCCA with GT1 - 5.
I do think BL is here to stay, it will take time for an alignment within the tech to happen.