Yes it would be nice & quiet under the approach chart.
Not so good for those living near the over run area though with all the noise of aircraft running off the end of the runway.
On a serious note 4 degrees is a bit too steep for most medium to large jets. I'm sure that lots of people can point you in the direction of statistics regarding the merits of stable approaches. One of the requirements being no more than 1000 fpm rate of descent. Sometimes this is not possible with slopes of up to 3.5 degrees so 4 degrees would be a non starter.
However there are a number of turbo props & a very small number of jets that are designed to operate into city centre airports where noise is super critical that can do 4 degrees & more.
Perhaps with time the normal (3 degree) glide slope will become steeper, as aircraft design evolves, but at the moment the safety issue out weighs the noise problems.