4 points I would like to make:
The Wikipedia article about Openwrt states the following text (within quotes):
OpenWrt supports any hardware that has Linux support; devices that can be connected (e.g. over USB) include
Mobile broadband modems
But much more to the point, if openwrt comes with a vanilla (or close-to-vanilla) Linux kernel version 4.14.195, then should it not already have all the packaged kernel modules within '/lib/modules' and all the hardware-autodetect features (and kernel module auto-loading) of the vanilla kernel?
And even if it is far from a vanilla kernel - routers now come with 512MB to 1024MB of RAM with the option of connecting a disk of any available size via USB3/eSATA.
So, space is clearly not an issue any more for packaging the same number of kernel modules that comes with most desktop distributions of Linux such as Ubuntu.
I just did a 'du -hxcs /lib/modules/"$(uname -r)"' on another Ubuntu (Desktop) computer to reveal that it takes disk space of about 237MB - So, this is well within the space limits of most routers made after 2016.
Not to be critical in any way (because this project is enormously useful in the amount of features/packages that it adds to routers, and so, has tremendous value), but this seems to me that it would be an obvious feature that users would want - i.e. to be able to use the router like a regular directly-connected virtual terminal linux computer.
This would make trouble-shooting any connectivity issue much easier - as you would not need to ssh in, in case you are not able to.
And if users believe they might have accidentally "bricked" their router, they might be able to verify that more easily by connecting a monitor and keyboard directly - if the monitor/keyboard does work to access the router's linux virtual terminal - then it is not a bricked router but rather a connection-related problem (which could either be a hardware problem or software-configuration problem).
It would also eliminate the problem of your router ssh connection disconnecting for the numerous reasons that it could.
You would also get to, in theory at least, see the router bootup messages when you reboot or poweron the router, and in theory, modify the bootloader command line much like a regular linux computer user could...
So, in theory at least, it just opens up the possibilities for much that could be done with a router that cannot be done easily right now.