It isn't really a huge buff. I think you might be interpreting the change incorrectly, as I also did when I first read it.
Lux can't detonate her E mid travel, it still needs to reach the predetermined destination. Lux just doesn't have to mash the E button to get the ability to detonate asap anymore.
Functionally, the ability is going to work the same; if the lux aims well on live now, its almost impossible to dodge E by walking. If this change goes through, that is still going to be true and you will still need a dash to avoid it. Nothing will really change.