Another option is NTFS, the one limitation is by default it is read only on macOs.
I would not understate that it is also very simple to write a driver for. The reasons for this have high overlap with the fact that the ondisk structure is crap. But it does mean that many people were able to write drivers.
Just don't use USB keys; they're terrible security-wise and you're forced to use technology built for your grandmother.
I don't use USB keys. I don't have any windows systems. But I do have UEFI, and that is based on FAT as well. Disregarding my grandmother's technical prowess, this technology is here to stay, and sticking your head in the sand about it doesn't advance any causes.
I live in an environment where I need to move files between several builds of Windows, Linux and macOS - and often where there is no network access because of security policy (misguided policy perhaps). Thumb Drives are the only way to function.
Oh, and the USB serial numbers of the keys had to be whitelisted on the secure network. What a fun that one was. They didn't even stop doing that after I showed them that I could modify the firmware of some of the sticks using software from some obscure Russian site and thus bypass the control...
(Does anyone know by chance how that website is/was named? All I remember is that it held hundreds of manufacturer tools for all kinds of USB stick controllers/flash chips)
It will also have have a workable implementation in what is essentially equivalent to the public domain, and be simple enough to process that hardware manufacturers can read it with a microcontroller.
I would love to see it happen, but I am not optimistic.