I doubt we will see anything to replace the C7 family for decades to come; the service rifle concept has reached most practical limits (the training and fortitude of the shooter is the determining factor in rife accuracy and pK these days).
If there is going to be a "replacement" we will probably see a C-7 A3 and A4, incorporating ruggedized parts, lighter weight components and changes to the stock and furnature to make the weapon more ergonomic, combined with vastly imnproves sights (including day/night or even thermal sights). After that, advances in technology and manufacturing wil make weapons like the XM-25 affordable for the infantryman, but we are probably looking 20 years into the future for an affordable m-25 type weapon and ammunition on the scale of individual issue.
A safe prediction wil be a support weapon patterned after the M-25 to suppliment the C-9 or M-203 much sooner.