SIG's idea is that the same chamber & bolt should be usable across 7.62x51 NATO and new 6.8x51, requiring only a barrel change to switch.
TFB First Look: SIG Sauer's Next Generation Squad Weapons -
From what I'm seeing, SIG is going all in for maximizing commonality in terms of production (their steel-based hybrid cartridges don't require the kind of changes to existing ammo infrastructure that something like GD's polymer cases or Textron's caseless ammo would necessitate, incurring significant cost-savings).
Plus, their rifle & LMG offers for NGSW appear to incorporate the AR-15/10-style layout for controls (fire selector/safety, mag release, bolt catch, forward assist...everything in more or less the same place you would find them on an M4)...should be pretty straightforward to get used to this for a US service member coming over from an M4 carbine and/or M110 DMR.