As a niche market the answer is yes in my opinion but it's far from mainstream usage if I recall correctly some altcoins use brainwallets as a default to registering them now but generally they are safe problem is the idea that people can rng it.
in an altcoin is using brainwallet by default then it is very susceptible to hacks. all the security of a private key is from its randomness and human beings are known to be incapable of creating random enough passwords. also the fact that such altcoin (if it really exists and uses brainwallet as we know it) is not yet hacked is because probably there has not been enough incentive to do it because of low value.