I am also looking for this. TP-Link stopped releasing firmware updates for this router, which it is a shame, since this router has a pretty decent hardware.
@acc did some good progress on investigating this router, following his instructions I was able to enable SSH access (despite of not being root). The tools he created to manually edit the configurations via backup-restore allows to change some configurations.
The interesting thing is that this router already runs a customized version of OpenWRT by TP-Link. So, it is my understanding that TP-Link shoud provide the source code of the factory firmware since it is usinn open source code...
Output from the stock firmware:
admin@AC2300:/root$ uci show | grep -i openwrt
luci.themes.OpenWrt=/luci-static/openwrt.org
uhttpd.px5g.commonname=OpenWrt
admin@AC2300:/root$