Latest information from Team Xecuter on running of roms is as follows:
"Copy the XCI files to the root of your Nintendo Switch microSD card so SX OS will be able to find them."
The Nintendo Switch supports FAT32 and exFAT.
Because some of the roms are very large and they go over the 4GB limit that FAT32 supports, that means you will either have to format the card as exFAT and then load them on:
(The switch upon detecting an SDXC card inserted will prompt you to download an update to use that format which will bring you up to 5.0.2)
Split files in the form of "filename.xc0" "filename.xc1" "filename.xc2" and so on to support ROMs larger than 4GB on FAT32.
There are multiple file splitters out there to do the job. A free windows utility is linked here:
http://www.filesplitter.org/Free-File-S ... 0.1189.exe
Load the file, select the destination folder for the files and the file size of each file you want to use. It hasn't been specified what filesize the SX OS will use, so i'll get back to you at some point when mine arrives.
There is a CDN download tool called "CDNX - CDN Downloader" that i think would have the potential to be able to download the specific updates required to download and install the exFAT package on the switch without having to migrate you to v5.0.2 but i haven't tried this.