No its not a full circle, not in rifles anyway.
Even if everyone decides that 223/5.56 is crap and removes it from military use and goes to something else, its going to be 308 or 45/70 govt, its still going to be a smaller (6mm, 6.5mm), bullet with a higher velocity.
Long range shooters still using rounds that are doing 3000fps+, none are going back to 200gr 2500fps rounds.
And just because the military might get a bigger round than 223, doesn't mean it'll die for civilians. Civilians ARE allowed to use hollow/soft points so a 223 rifle will remain a nice light, low recoil lower noise hunting rifle.