The regular ISO approach with mhwd might be the wrong idea. For the special use case of a gaming console, the OrangePi Neo, we developed Manjaro Summit: Manjaro Summit public Alpha now available
It is image based and if needed with branches. Based BTRFS you will load tested OS images and keep the user data. Additional you can add package overlays or flatpaks as applications. Alpm (pacman) is not used. Updates are handled via arkdep.
So you configure the image as needed with the proper drivers preinstalled. And when an update is ready the whole system is changed.
Even updates after 3 months not touching the device should work, plus you can configure how many old images the system should keep for rollback.
What you need is a package repo for your additionally added packages not provided by Manjaro and a file server for the images.
Install media can be a live ISO or a disk image.
This way you configure it for the specific usecase. OS is read only with the option to unlock the rootfs.