MU-MIMO?

Four more years…

And so it came to be…that many more years have and most probably will pass xD

MU-MIMO is work in progress according to reinis from MikroTik:

6.41rc support AR9888 chipset?
Do you have any information?

Might have been nice if they ever got it working.

From http://forum.mikrotik.com/t/802-11ac-wave2-support/127501/25