Great link!
I asked the question because "FT over DS" seems broken now 
https://forum.openwrt.org/t/802-11r-broken-in-recent-master-nl80211-attr-sta-vlan-errors/88888
I do not have a controller, so I wonder how the APs talk to each other or "over DS" without some sort of controller just doesn't work?
provided that both APs have a way to communicate. In a controller-based network, no problem.
And from the comments:
I haven't tried 802.11r with standalone APs, as I have a controller. So I can't say much about how (or even if) it actually works, and it's probably somewhat of a corner case, as most people do have controllers anyway.
The best way to make this work without a full blown WLC is probably to look at Mobility Express feature on the new APs, which in 8.2 allows you to run an AP as a cut down controller of sorts. In 8.2 this now also supports FT.