Hmm, perhaps. I guess it would be something like:
Get homebrew -> dump necessary stuff -> when update hits, don't update immediately -> wait for release of exploit in downloadable title -> install exploit, built using stuff dumped from NAND -> update -> reinstall homebrew
The main problem I see with it is that it probably would require about the same amount of effort to find an exploit in a downloadable game as in a cart based game, and to much lesser benefit. So it would be more sensible to just try and find another cart based exploit (or even better, system software based exploit, akin to bannerbomb and letterbomb on the Wii), rather than waste time on an exploit that will only be useful to a handful of people. Of course, the exploited title would also have to have been installed on the console before the update was released I'd assume, which would only be by chance.
In addition to all that, reinstalling any sort of homebrew loader would require a new kernel exploit, which it would be foolish to waste on a userland exploit that only a very few will be able to use. Again, it would be more sensible to couple that new kernel exploit with a cart based exploit.
In short, I'd say the only real "benefit" of being able to edit SD savegames would be for the sake of save game based cheats (increasing money, items, etc.).
