@Blaquespell 

Both models the Archer AX1800 and Archer AX20 should be the update.  They run on the same chip so its possible.  If the unit had different chipset then we would not be able to say the same.  Please note though the update is only 'Planned' and not a guarantee.  We cannot gaurantee any planned feature will actually release until the R&D team releases the frimware.  Until that point the plan is open for modification and or reconsideration. 

@Carl Well let me ask you this. The AX20 V1 no longer says "planned" on the OneMesh page of your site. I clicked on the AX20 icon and it takes me to the firmware page for the AX20 with firmware Archer AX20(US) V1.0 200929. This firmware includes the OneMesh update, but looks to be only for the AX20 V1 and nothing else. Since I have the AX1800 V1.2, is it just a matter of time until it's available for this router, if they are running on the same chips?

@Blaquespell 

Yes i would so. New content is typically added every Friday provide it is not a holiday or PTO happening. OTA updates are generally added frist since they are simply on the cloud server and manual updated by the EOB that day.   I would just continue to check back as the update is likely soon.