.223 /5.56 is king IMHO ( as is .308 ) .... mainly due to cheap milsurp cases. and cheap production ammo. ( .223 and .308 is probably cheapest you can buy )I can buy pmc 5.56/ .223 for approx. $6.00 a box, and kick the shit out of coyotes. or load a bt bullet into cheap lake city brass and kick ass... IIRC .204 uses a .223 case necked to approx. .20 cal. again, cheap cases, you can neck down. ( well maybe not .204.... but you could make .20 tactical out of .223 cheaply, and kick ass, if you were inclined )

I love new calibers as much as anyone... but my first loyalty belongs to my wallet, and what I can get for that price increase. for me, its just not worth it, except maybe in a limited role, for a specific purpose. .204 would likely do that. and ( .300 aac for example).  I could see people wanting this for a varmint / hunting rig... hell maybe gov sponsored military round on a small scale.... just not me.  the price of new brass and ease of finding ammo would make it undesirable all by itself.

And that's the very point I was making.  Every cartridge gets its start somewhere.

Its interesting but ammo cost/brass cost would make it prohibitive for a plinker.  As a dedicated coyote rig it or pushing heavy bullets for deer/long range target it would add 100 yards to the 223.  Perhaps more interesting is could this be necked up to a 6.5, 6.8 or 30 cal and get the same performance as the 6.5 grendel, 6.8 spc, and 30 ARK/30 Herret all while only requiring barrel change and 6.8 mags.  Basically will it equal those rounds while keeping the same bolt carrier group and then will nosler make additional rounds.  I can tell you right now a 30 cal ar-15 that only needs barrel and mags that can get 2400 fps out of a 150 grain bullet and 16" barrel would sell.