Not much concern for the Challenger, it's an old car, both in platform and looks, and has it's own niche following.This is a sales thread so lets talk sales from 2015 through Feb 2018
Mustang beat camaro by 93985 cars
Mustang beat Challenger by 116025 cars
I think this shows what the buying public wants not a boat and not a look like the old car pill box. The S550 Mustang is the preferred car.
About the camaro, I'd be curious to see the overall trend vs stang in both 5th and 6th gen. Basing on 2015 forwards, it's not really fair since the 6th gen was introduced a year later.