Would Android 4.3 mount exFAT formatted external SD card automatically without additional software?
exFAT support is kernel based. open terminal and run
if in the subsequent listing you see
your kernel supports exfat file system unless the build is skunky. if the in the listing you see
then you don't have exfat support.
In one instance i've seen, even though the kernel may have exfat support, the rom may not, or it's "broken" in some way. As to the formatting of the card, i believe it needs to be formatted exfat and unaligned.
Else, it should mount like any other external card with one exception, the entry in your fstab for the external card. If the entry for
is vfat, then you may have a problem. The entry should be auto or, if you know how to unpack and edit, then repack and flash your boot.img, you can specify exfat.