IMO Russia will switch to 155 mm for their medium howitzer. It's easier ammunition wise because they can get ammo supply from allies like China and Iran which use 155 mm. 152.4 mm is very ancient and dates to pre WW1 British 6 inch howitzer which Russia bought from Britain before WW1 but now only Russia still uses that caliber which is difficult logistics wise because they cannot get ammo supply from allies because they all use 155 mm.