I've gotten this question a few times. "Would SDcards make a good ZIL device?" "Would SDcards make good ZFS devices?" The answer to both is resoundingly no.
The reason for this is simple, and is the same reason you should never reformat SDcard media using your computer.
It boils down to the fact that you need to do some very "SDcard" specific optimizations when you layout your filesystems in order to get good performance. (The details for this are only available after signing an NDA with the SDcard trade association, btw.) Of course, general purpose computers use general purpose filesystem code, which is targetted for hard disks. So the optimizations, if there are any, are all wrong for SDcard media. (Note that this only matters when doing the initial filesystem layout .... i.e. when you are formatting the media.)
You can reclaim at least some of the performance you might have lost if you've made this mistake, by reformatting the media in your camera. But unless you have a much fancier camera than I do, your camera probably doesn't speak ZFS.