Personally, I hope with Regulus getting re-integrated into the League we get a Merkava Mk X to become the main battle tank of the FWLM. It really lacks something of theirs produced in that weight range and the assault tanks are no great shakes either. IMO it is the only candidate until Andurien comes back with their Moltke. Or have they picked up a Kinnol line from the Republic break up?
And yes, I would love to drop a Fox built Gauss Rifle in for the Light Gauss that rests in the turret though I think the SSRM would have to become a SRM, Clan SSRM, or shrink a launcher size to get more Gauss ammo.