I have yet to be seduced by the sub caliber cartridges from .12 to .20, despite having been tempted by .17s from time to time; the Hornet variety and the Fireball variety. To my way of thinking, the .204, particularly when built on an overbore cartridge case, does nothing the .17 hasn't already done. That's not to say it isn't a fine cartridge, after all, it shares the same ballistic niche as the .17s, and undoubtedly, their short comings as well. In a typical sub arctic breeze, the .17's drift is measured in feet, rather than inches, and I'm confident the same will apply to the .204.
Having said that, I wish the .204 long success and popularity. It provides me with an unlimited supply of brass from which to make .222 magnum, which is the best of that family of cartridges. It has about 5% more capacity than the .223, combined with the long neck of the .222, giving it the advantage, but the popularity of the 5.56/.223 has pretty much spelled the doom of this fine cartridge. Fortunately though, the folks who brought us the .204 had the foresight to base it on the .222 mag rather than necking down the .223, and that makes me a happy man. I hope the .204 becomes the most popular varmint cartridge of all time.