Had a quick look around.

The package you've downloaded, "usb-stick-utils-automount-exfat-support",
is a different script ("mount-usbstick.sh") that gets triggered (see "90-mount-usbstick.rules") whenever a USB stick is inserted (either a microUSB stick directly into the USB OTG port, or a regular USB stick into a USB HUB conencted to the OTG post).

It does support exfat, but does not react to SD cards.

the built-in script that gets called is "mount-sd.sh".
If you have a look into it, it doesn't handle the FUSE exFAT module.
(compare the 2 "case ${TYPE}" switch blocks in the middle of both scripts).

Together with TJC member "V1olat0r" we had bounced back and forth a few more advanced scripts (handlind NTRFS, Swap, etc.)

I think you should be able to get SD card automounting by transfering the vfat/exfat/ntfs case block from "/usr/sbin/mount-usbstick.sh" to "/usr/sbin/mount-sd.sh".