Our MSI B350M can support 64GB with the R5 2400G using 16GB sticks which is actually our target for the machine. With available 16GB sticks this can be realized but the BIOS may need to be updated to handle the higher speeds. More recently 32GB sticks are available but so far AMD has not responded to inquiries.
G.SKILL 32GB DDR4-3000
More conventional 16GB sticks are made with 16 chips of 8 gigabit which is what Samsung is making now. G.Skill has some 32 chip memory sticks for Intel X390 which is now the largest known memory capacity. The Trident Z RGB DC memory modules stand taller than the classic Trident Z RGB modules in order to accommodate the increased number of DRAM chips.
Samsung has recently began shipping 32 GB DDR4 unbuffered memory which would make 128 GB possible. Samsung is using 16 gigabit memory on their newest line which will bring a new cycle of upgrade possibilities. At present all the 32GB sticks are 16 chips per side.