The M4 is NOT going away. The era is not ending. The XM7 and XM250 are only getting issued to combat arms troops. And even then, I suspect leaders, grenadiers RTOs, medics, etc will still continue to use M4s.
I’m “meh” on the XM7. I think it, along with its cartridge and XM157 optic will be great to outfit the rifleman position in a fire team, and maybe the team leader. But everyone else should retain the M4. The XM250 on the other hand is so amazing. Lighter than the M249, even with a silencer on it. And much, much better external ballistics. Ammo weighs more, but some units already use the 7.62 Mk48 instead of the 249 anyway. So that ammo weight will stay the same.
Do you think they would have troops in combat together using different platforms that take different mags and different ammo? I was under the impression that it was a priority and it was important to keep that stuff the same. My knowledge is very limited on this subject.