This has bothered me for several years. One of the beauties of an electric car is the lack of noise. Humans have a strange relationship to sound. I see many articles where people want cars to sound like cars, yet I have friends who are surprised that my robotic vacuum (Roomba) is "so noisy". I stand on street corners and feel assaulted by the noise from dozens of idling engines providing no useful work and wonder how nice it would be to drop the sound level on our streets. It's noisy now with lots of idling internal combustion engines, but imagine if we have dozens of different noises, all customized from regular engine noise, futuristic space noise, to Nyan Cat. Is this the sort of environment we want? Cacophony.
I am sympathetic to the plight of sight impaired people, they currently rely upon sound, but quiet vehicles already produce problems for them, and as drivers we MUST be careful of ALL pedestrians. I'm not sure the solution is to replicate old technology by imitating old noises. There must be a better solution than hacking something on to a relatively clean and simple system.