Are you sure new large cards you get are F2FS ?I used a 256GB card in my Pandora regularly. The catch is that you'll need to reformat the card to get the best use out of it. From the store the large cap cards are F2FS.
You are correct and my brain is gone or there are too many file systems to keep track of these days. Big cards are exfat. The Pyra prototype has an F2FS on the microSDXC card that I had been using internally. Wires crossed.Are you sure new large cards you get are F2FS ?
AFAIK standard filesystem for SDXC cards is exfat.