New Cartridge Developments and Implications for Dismounted Infantry Soldiers

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Had a question on this.

while we are mostly in agreement that we need to move to a 6.5mm cartridge, there is some question as to whether we stay with the current M4 platform thus using a round like the 6.5 Grendel (6.5x39) or go to a longer round like the 6.5x45. Or do we go to something new like a 6.5mm CT round?

Since smokeless powder was adopted in 1892, the Army never adopted a completely new cartridge specifically to upgrade old weapons.
So, I think it is rather unlikely that the M4 platform would be kept and converted to 6.5 Grendel, if that round were to be be adopted.

CT ammo would be preferred over brass-cased cartridges like 6.5 Grendel, but it remains to be seen if it will ever be ready for fielding.
Even if CT technology does someday reach that level of maturity, it is currently uncertain what caliber(s) would actually be adopted.
The CT carbine is being developed in 6.5mm, but the CT machine gun is 7.62mm. This says to me the Army is not sure what it wants.

And do we also go to a .338 round like the .338LM (8.59x70) or .338NM (8.59x63) in a MG that then allows the .50 M2 to be retired?

I doubt that .338 LM/NM would be a viable replacement for .50 BMG, except for a few special purposes where weight is a critical factor.