This is an R/F device, therefore regulatory certification like FCC or local equivalent is imperative for legal distribution of any custom designed solution. If not approved in a given local jurisdiction, legal distribution would be impossible and the first to launch a complaint to authorities would be the name brand vendors, therefore causing a ban/seizure of illegal hardware at the import level.
Unless OpenWRT is willing to undertake such expensive certification process cost, the custom design discussion must come to an end, period.
The only other viable solution would be pre-certified white box label of pre-existing/certified designs, bought in batch process. However, in my youth, I must have overseen the assembly of thousands of clone PC'S with parts manufactured by known Asian manufacturers. I can vouch the fact that quality/flakeyness of various parts/components varied very much depending on manufacturer, product and production run/batch or even revision for that matter. In the end, a very risky endeavour for OpenWrt.
In the end, it would probably be wise to just pick a half dozen commercially available products and make sure they are properly supported.
For example the Linksys EA8300 is supported, has ample RAM and Flash, decent SOC, tri-band and more importantly dual failover boot/firmware partitions. The R7800 seems to be a very popular device as well. The Rock Pi E and NanoPi R2S have descent SOC, RAM and unbrickable due to removable Flash, however if they were better supported, I am sure their popularity would skyrocket.
In the end, it's about KISS, Keep It Simple Stupid.
There are several devices out there, addressing different market segments/requirement, it would be wise to maybe figure out a short list of devices and just support them to death.
KISS... It's not about reinventing the wheel, it's about picking up a good set of wheels and having a good drive...
Just my two bit rant...
Edit: The MR8300 is basically same as EA8300, except more RAM, therefore supporting to death families of a short list of equivalent hardware, makes for more choice as well.