Implementing a whitelist is going to be hard, because there have been so many releases that its simply impossibly to fit the entire database into an isolated loader, and streaming one in leaves more room for bugs to creep in.
And updating metldr will be a nightmare, current the update process is entirely offline, because not everybody has their console connected to the internet which means Sony have to remove yet another feature. And Sony is not going to want to do that until they have worked out how on earth geohot exploited metldr for its keys, which is probally why the Temporary Restraining Order is demanding that he should turn every single computer or disk that he has to sony. Also, there is no way to revoke metldr. If you have a valid metldr for your console you can downgrade.
So yes, it might be possible for sony to patch things up, but it will be really, really hard.