Read about NGSW a long time ago in detail,all short listed systems have pretty slim chance except MCX,that to if adopted in limited number.
Talks of Cal and Rifle replacement goes back to late 90's with XM-8,OICW,6.8 SPC,6.5's,.300 blk to name a few choices examined and discarded over time.
Any new system brings nothing new at table and with huge amount of 5.56 and x51 Nato ammo sitting around,these cals are going nowhere else.
P.S:-Read about 7.62x54R it's oldest and only rimmed cartridge in service in 21st century,post WW2 it only survived in USSR due to sheer amount of it lying in USSR depots.
their is a Reason why all modern armies have moved away from Lethal Heavy Rounds to light less deadly ammunition.
The Western Countries moved away from 7.62 x 51 NATO to 5.56 x 45
While the Eastern Block moved from 7.62 x 39 to 5.45 x 39
China from 7.62x39 to 5.8 x 42
-Modern Ammunition is Light weight and hence easier to carry. Soldiers can carry more ammunition. i.e Higher Carrying capacity per soldier.
-Modern Ammunition is less lethal, Causing the Enemy soldiers to carry huge amount of Wounded incapacitated soldiers.Wounded soldiers are a massive toll on battle field for fighting armies compared to dead soldiers.
-Modern Ammunition have higher Muzzle Velocity ( Jacket of 7.62 NATO is more then twice as heavy as 5.56 NATO)
-Less Recoil
As for New Guns. Imagine a G3 vs CZ Bren 2.
CZ Bren 2 can be adopted for both left and right handed use, Its Mag release and Slide lock are on both sides, It is much lighter, It has built in 4 Picatinny Rails for Detachments, It has Folding Stock, Rubber Butt Stock grip.
Easier to handle, Easy to maintain, customization to Soldier's Preferences, More Ammo per soldier, You don't need to drag the Type 56 along with G-3 If you can adopt a single modern standard Rifle.
The Existing G3 Stock and Ammunition can be phased out to Paramilitary, Reserves and Law enforcement forces. And For the Love of God Get rid of those Ancient T-56 Rifles of the Police Forces. AK/T-56 are Favorite rifles of Thugs and Outlaws, An Industry is running for AK style Rifles due to Use by Law enforcement. Scrapping the T56/AK will do more good then harm. Arm them with G3 and Arm the Armed Forces with Modern Rifles and Calibre