Reducing the weight is a interesting idea, seems like it should work.
Alot of chime plungers have the center drilled out.
On the same thoughts on making plungers faster, I have wondered about this- could the air trapped between the plunger and the coil stop actually slow down the travel as it needs to escape when energized? I have thought about drilling a small hole it the coil stop for air to escape. Not sure it would make a difference. Drilling a hole completely through the plunger would do both- reduce wieght and provide air release.