Well it’s a public forum and that discussion that I linked has been there since 2014.
I am on mobile so I can’t easily search but IIRC David himself has said that once the network gets larger it will be difficult to create that kind of attack and I agree. It’s easy to envision a laughable scenario with 500 nodes, but with 10,000 nodes that also have to earn basic reputation by behaving well, that wouldn’t be easy.
At the same time, like I said on that linked comment, I don’t care if the attack is merely “possible”. If you need a backup, make a backup. Or post 2 or 3 copies.
Nobody designs storage (or anything else) to be unbreakable. There are costs to consider. Nobody should be required to pay for 28 copies of all chunks, just so that people with large files can get six nines.
Half-baked idea: vaults are filled with real data and those are checked, that’s how it works by default. Redundancy is not faked or demonstrated by vault - it has only 1 copy of those chunks that were entrusted to it. It doesn’t know jack about the rest and whether those other nodes/vaults are lying. That is performed by other node roles in SAFE. Each vault takes care of its own business.