The list of games is updated
before the game is loaded and the save is made
after the game is loaded and the OS is no longer present, and can't write to SD.
Not a great idea. There already is a flashcard on the market that does this and its constantly being criticised for that because if the inherit issues this comes with. The Ezflash omega does write the contents of SRAM to the SD card once it changes (I.e. the in-game saving has concluded.)
But write operations to the SD card take time and when you interrupt this process (by powering off the console), Filesystem corruption will occur. Yes, waiting a few seconds after the process has finished in-game is not an issue at all, if you know to do that.
I understand you would want this as an option (not the default or even the only method) but I do see an issue with implementing this as an option for people who don't know the inner workings of these things: people *will* enable that option and people *will* suffer Filesystem corruption and lose their saves. They will be disappointed or even angry and they will fault the everdrive for an "unreliable" option.
The effort to implement this and the risks/downsides that come with such an option far outweigh the benefits it has, in regards to the average consumer IMHO.
Flash wear would be another concern as writing to the SD card that often would waste its limited amount of write cycles. It's strange that the SD2SNES doesn't got the same complaints as the Ezflash. Maybe it's better at preserving the save file by keeping backups? If it detects that the game is using the SRAM as extra work RAM it will not update the SD card every single change to reduce flash wear, but it will save backups of the SRAM periodically, so it's probably wearing out the SD card faster than Everdrives are.
The current design of the Everdrives is understandable and I don't think it's really a problem, as long as you regularly make backups of your save files (which you should do regardless). You will only loose your latest play session once in every 20 years when the battery dies, that's still better than on real carts where you loose it all.