I meant they could blacklist an specific game cartridge for all 3DSes. And I am pretty sure they can also brick an specific 3DS, I know they won't because of law issues, just like Microsoft won't brick your computer for using pirate software but doesn't mean they cannot only that they may not.
The way this infrastructure works is that servers in given regions
"raise" a flag with the latest firmware revision number. Upon connecting to the service, the 3DS verifies whether its firmware matches that value or not - if it doesn't, it begins to download said firmware and once it is downloaded, it starts bugging you with the update prompt because it's a legal requirement to ask the user for permission.
This works in the exact same fashion on the DSi and in no way allows bricking a specific 3DS or DSi
without hard-coding which 3DS/DSi they mean in the update itself. This is not being done because it's a hassle that'd artificially inflate the size of the firmware by adding more and more offenders to the blacklist.
DS games with exploitable headers used for launching flashcarts on the DSi were blacklisted in the same way - the list was embedded into the firmware. The problem here is that there's a handful of
"offending" games wheras
"offending" gamers can be counted in millions and even if you
do create a blacklist like that and miraculously find space to keep it, you have to keep all the offending numbers
for good because you literally have no guarantee whatsoever that the offending users will agree to an update... which they have to agree to as a legal requirement.
It is infinitely easier to disable a given eShop account, thus invalidating whatever content was purchased on it
or banning a user server-side using an account system
(which the 3DS does not support - it only supports eShop accounts and only server-side, the rest is still handled with generated Friend Codes).
The method you refer to is technologically feasable, however crude and ineffective enough that you'd have to be an idiot to choose it over far better methods of banning and suspending, much like it's technically feasable to juggle pork sausages using your ears except juggling rubber balls with your hands is probably much easier and usually yeilds better results.
