But you’ll lose the ability to perform the 3-LED and 4-LED reset (i.e. rollback to previous/factory snapshot when something goes wrong). But it’s possible this limitation will be overcome in the future.
I suggest you to read through Writing to mmcblk0p1 concerns - #15 by vcunat - SW help - Turris forum , where a forum user did monitor eMMC writes and it seems they managed to track down the last thing that was periodically writing to it.
Of course, if you want to store suricata logs permanently, you’ll need a device to write them to. The router tries to move all this data-intensive stuff to folder /srv, and there is a Foris plugin called “Storage” (installed by default) that makes it easy for you to select an external drive and move all things from /srv to this drive. If you set it up correctly, all periodic or intensive writes should be on the external drive.