I already tried a 16gb microSD from an older gopro in FAT32 and works.
Two things still troubles me.
Since webos is linux based, why shouldn't support exFAT since is getting a common format for also very common large memory cards.
the second is since GoPro connects via PTP exactly to prevent file systems compatibility problems, why can't webos read both photos and movies? PTP is everyday used on smartphones and other devices. GoPro on PTP connection works fine on computers to download photos AND movies. I don't get it why webos only sees the photos...