Make no mistake.File-based emunand are still prone to corrupt. Make no mistake. While they are supported they are not stable. Just like ExFat. Partition based are still better.Since almost 6 months now the EmuNAND on files are well supported and fast as a partition. Read the Atmosphère release page
I'm using Atmos with a file emummc for the past few months without any issue, I've used exFat since day one on my switch and the SD Card still reads without any corruption after a few years so I guess this really is about how often do you write/delete stuff rather than "YOU CANNOT USE FILES or EXFat" speech....
Why not just convert it? Its easy. I would convert the sx emunand to an atmosphere nand. Then make a second hidden partition emunand for sx. Shrink it down to 8gb for saves and make super XCI out of the games. The whole SX install takes 8GB on the SD. Both SX and Atmo have their own hidden partitions. Could add ubuntu and android partitions too.Yeah sure, makes sense...I would tell him to do partition emunand as well...better safe than sorry...But my point is that you are too sure that corruption will occur and maybe it won't...If my ExFat card that I still use for SX OS gets corrupted now after 3 years... so be it...everything there I've played to my exhaustion, I would format and start again...