Thats a good question and i also read such posts on other threads regarding exfat.
I have my 400GB microsd card on exfat + SX and never experienced any problem within SX + XCI or any other homebrew app except one:
Retroarch 1.7.5 crashes very often just during browsing of games and so on... (during it loads preview images and so on)
Dont know if it's related to the exfat "issue" discussed in other threads or just small bugs /glitches of RetroArch (because it was just released officially).
Would also be interested in an technical proof that exfat is the issue on retroarch,
and if a switch to fat32 really solves the issue.
thx
pOpY