1) 802.11r
In it's current form, 802.11r is well-supported by OpenWrt (as long as the underlying WLAN driver/firmware can parse Mobility Domain Information Elements). It is practically 1-click config in LuCI for WPA2-PSK and as long as both APs have the same SSID. For me however, I need an additional step where I switch FT-over-DS to FT-over-Air because I get the following error with DS (maybe because I don't have a controller):
NL80211_ATTR_STA_VLAN failed: -2 (No such file or directory)
2) 802.11k
The switches to enable/disable are in mac80211.sh and thus can be enabled/disabled in the /etc/config/ folder. However, a script has to be used to be able to pull in the information required by hostapd to generate a neighbor report.
At least on ath10k(-ct) & ath9k, it works:
3) 802.11v
Whilst again, the switches exits in mac80211.sh and thus can be enabled/disabled in the /etc/config, there is no script/logic that fills in the required data. @PolynomialDivision is working on it through a de-centralized controller, DAWN for this (which now exists as a package in OpenWrt snapshots). But @anom3 has also built a set of scripts which also aims to do the same.
My experiences are limited to ath10k & ath9k. I know that mwlwifi does not support anything beyond 802.11r. I am unsure of the current state of support for anything else like brcm or mt76.