Soldier Systems Daily posted that US Army is in early stages of looking for an intermediate caliber(.260, .264 USA and .277 USA) for general issue. Nothing is set in stone and even if the adoption happens it could be decades away.
In the meantime, an option is to use 7.62mm/.308 WIN, which are plenty in inventory.
http://soldiersystems.net/2017/04/05/us-army-considers-7-62-interim-battle-rifle/
There is more to this than just the ammo and firearm, so read the article to get a good feel for complexity this change could bring
You can also read commentary from The Firearm Blog
http://www.thefirearmblog.com/blog/2017/04/05/breaking-us-army-considering-going-back-1954-interim-7-62mm-infantry-rifle/
From: Soldier Systems Daily, The Firearm Blog
