Indeed, linux kernel is modular, so adding support for another FS is a matter of compiling a module, then inserting it.
Did you try to use an ext4 formatted sdcard ?
It could work, as ext4 is seemingly already supported by the FP2 :
cat /proc/filesystems | grep -v nodev
About ExFAT, remember that it is a Microsoft proprietary licensed format. Would you want to pay your FP a few € more for using this ?