First of all I do not have proof of 4x4 mimo BUT Telkom and Rain run 4x4 mimo and some cases massive mimo setups on their towers especially on their TDD bands. You will see this is especially true for Telkom which uses the flat rectangular sector antennas. Look at the cables at the bottom. It would give an indication of the towers 4x4 mimo capabilities. Very interesting. This is where Samsung s8,s9,s10 and upwards devices and B618 Cat18 and higher would support both 2cc and 4x4 mimo. If you aggregate a band with 2x2 mimo with a band with 4x4 mimo the mimo mode will fall down to 2x2. I do not know if each device has enough radios to support it or if there is a minimum standard to meet I would need to research more on that.

I know for a FACT that Telkom broadcasts LTE on 3 frequencies and 2 bocks of spectrum on the one. Band 1 - 5MHz x 2 FDD, Band 3 - 10MHz x 2 FDD, Band 40 - 20MHz x 2 non-contiguous. Telkom aggregated B1+B3 and B40+B40.

4x4 mimo or massive mimo on LTE has a theoretical max higher than say 2x2 mimo with 2 carrier aggregation. 4x4 mimo squeezes every bit of bandwidth from that tower so much more efficient than say a 2 carrier aggregation that will likely see a higher peak on a speedtest.

I'm using Telkom and Rain networks as examples as they both operate both FDD and TDD bands on LTE and aggregate them and implement mimo on them. One very interesting statement from Rain to me is that the more cats the better even if the lte combinations aren't supported the chipset has been improved. Better chipset means better carrier aggregation performance. Telkom with their 2x 20MHz spectrum in Band 40 is the perfect example of how the latest chipset is SO efficient at aggregating the two spectrum blocks giving great performance.