I think I answered my own question in this thread: Support for D-Link DIR842 (Rev C3) - #77 by augs
The version I have seems to load boarddata from the firmware image provided by dlink, not from the art partition. I've got mine mostly working by commenting out the caldata_extract line for this model in /etc/hotplug.d/firmware/11-ath10k-caldata and copying boardData_2_0_QCA9888_5G_Y9582.bin from the vendor firmware to /lib/firmware/ath10k/pre-cal-pci-0000:00:00.0.bin
I spent about 20 minutes reverse engineering qca_ol.ko, but didn't make it far enough to understand what the offset in the structure was for the ID it was mapping in ol_ath_softc_net80211 (this changes based on various compile time flags). Someone who is more familiar with qsdk could probably figure out the image selection fairly quickly.
I'm also not sure what the stance is from openwrt of including boarddata from the vendor directly in the openwrt source tree and what the copyright implications are.