The XM25 is not a rifle. It's a grenade launcher. The "advance" here is in the fusing of the projectiles (impact, delay, VT).

It will be interesting the basis by which this will be issued. I suspect it'll be issued at about the same density as the M240B (given its cost, and the logistics of the ammunition) and to Infantry units primarily.

Although the ability to select the munition's fusing is a notable development, I wouldn't want to be the guy to have to give up my M4/M203 for something that does just one thing. However, I would be highly surprised if this weapon were to completely replace the M203, for which both the weapon and grenades are considerably cheaper, though probably more difficult to maintain proficiency with.