The US Army has said they have no interest in the Marine's M27 rifle, and they are moving ahead with the next generation weapons that will feature case telescoped ammunition with the ability to defeat ceramic body armor beyond 600m.
If the M4's in service are still in good serviceable condition, then this is probably the right call. If they are worn out after 17 years of war, then perhaps this isn't the best idea.
Sadly the Army has been ready for the next generation weapon since the day we adopted the M16 over 50 years ago. So it will be interesting to see what the future holds.
Ballistically speaking, something will have to be done, and done soon. Because cheap, readily available body armor is showing up more and more on the battlefield, and our 5.56 can't penetrate it.