Well, to get my impressions on it.. Ocarina/Gecko OS staff developer speaking here (and many people say I would have developed Ocarina alone - let me just assure you I did not)..
From a theoretical viewpoint this can be even patched by Nintendo.. however, I agree it's VERY hard.. to make it short: Brawl uses IOS36.. IOS36 is real time surveilling Brawl.. they could release an IOS36 upgrade which overviews Brawl and could stop the stack smash. Indeed even Gecko Cheat codes could probably make this exploit unusable.
However, this would add a new level of competition even for Nintendo.. it's more likely they destroy all entry methods of installing homebrew on the Wii. We could then still run homebrew directly using the exploit.
So well.. it's not unpatchable.. but seriously much harder than before!