the stated solution is to "load the file contents into RAM at system bootup"

Wait, so you want games on your hard drive because SSD space is too expensive (~55€/TB), so then you permanently occupy some RAM instead (at ~6500€/TB)?

Have you tried doing a linear read from disk instead, like to use zstd for good compression and fast decompression of the Factorio data folder and then make a Factorio shortcut that does like:

    $ cat run-factorio.sh
    mkdir /dev/shm/factorio
    cd /dev/shm/factorio
    tar xf ~/games/factorio.tar.zstd
    /dev/shm/factorio/bin/x64/factorio
    # the above line will block so long as the game runs
    tar c . | zstd -T0 -19 > ~/games/factorio.tar.zstd
    echo Finished saving Factorio data back to disk

such that all reads on startup (and beyond) will be from RAM but only while you are actually running the game?