You'd still have an E to A size so it's not a one size fits all. Cost, power usage and heat all play a part. And yes, it would help to free up a smaller ship by one slot maybe making it a more viable ship for exploration. I don't own one but the Asp Scout is a good example. This build:
https://s.orbis.zone/1569 One visit to Felicity and you can make it a reasonable exploration ship. If the G FSD booster was in the utility slot it would put the jump range in the upper 50ly range and now you have a ship that many feel is useless is now a pretty good exploration ship due to it's jump range. So a good looking ship thought of as somewhat useless now becomes useful in a more specific role.