Right, I've read it again. Please find my comments on it below.
So its either Beamforming or Spatial Multiplexing .... normally part of the wireless driver packaging
Well... Yes, spatial multiplexing is the technology that MIMO is based on, and that must be implemented/supported by all 802.11n and newer APs and clients with two or more chains. It IS supported by almost all currently available Mikrotik WiFi devices (except single chain devices like Groove, obviously). Beamforming is a requirement for MU-MIMO. Beamforming is NOT generally supported on devices without support for MU-MIMO, with some exceptions.
Very few MIMO clients support Spatial Multiplexing because its expensive to implement
Wrong. All 802.11n and newer devices (both APs and clients) with two or more chains must support spatial multiplexing. That's basically how MIMO works.
BUT Beamforming is very widely supported because its CHEAP
Wrong. Only a few vendors support beamforming in their 802.11n and 802.11ac wave1 devices, and those devices are usually pretty expensive.