Wow.
Do you realize what the range of a 300 blackout is? I hunt deer with a suppressed 300 blackout so I can tell you....about 80 yards. Beyond that it falls apart and is practically useless, yet you want to replace the entire inventory of infantry rifles with it? I want to be on the side of whoever's fighting you when the next war breaks out.
The 300 blackout kicks about the same as the 5.56, which is practically none in either case. Barrel life is a non-issue, if you can wear out a 5.56 barrel or a 300 blackout barrel then you've shot 1000X more than the average soldier will shoot in his career. I'm on my fourth 22-250 barrel after shooting untold thousands of rounds at prairie dogs and it's not particularly a barrel burner round. If you want to wear out a barrel load a 220 swift to the hilt and shoot it until the barrel almost glows. You're not going to wear out a chrome lined military M16/M4 barrel in your or my lifetime, and I doubt anyone will be able to wear out a barrel of the new round. It's a non issue.