Does the Keysight solution support the 4x4 MIMO tests for LTE TDD?

Yes, the N7625B can make downlink MIMO configurations (up to 4x4) with static fading including spatial multiplexing with CDD (cyclic delay diversity) and transmit diversity. The 89601A-BHE can support the 4x4 MIMO analysis using Keysight Oscilloscopes.