Thank you. The AC4000 version of this very router is the A20 that I am currently using and am not crazy about.
To be clear: You're saying that OpenWRT does work on the Archer A20? It's not on the list at https://openwrt.org/toh/start. It would be exciting if I can throw OpenWRT on this router!
Also, if I was to replace, hoping to go AX for future proofing.