If I understand it correctly, you are now saying that someone would DDOS the entire gossip network, completely halting any more production of blocks so that their slashing doesn't go through?
We're not even talking about "nothing at stake", or anything having to do with PoS anymore. We're just talking about a massive DDOS of an entire network. Node operators in PoS networks, as well as Bitcoin, have ways of dealing with DDOS which are the same as how anyone deals with it, and I don't need to get into them here.
If someone was able to overcome these DDOS mitigations and completely prevent a PoS network from receiving any legitimate transactions, they could do this to Bitcoin as well.
Who will record this "evidence" to the blockchain? Anyway there will be two versions of the blockchain. In one of them attacker's stake was not slashed and there is no any "evidence" of his malicious actions.
Not sure what these two versions of the blockchain you're talking about are. Signing two blocks at the same height with the same chain id is the slashable offense. It doesn't matter what's in them.
If the attacker wants to have his own blockchain off in the corner where he has all the money, nobody cares.
Really?! One version is "Vitalik's fork" and another one is "non-Vitalik's fork". Which one of them is a valid chain? Any idea?
Assume the attacker is Vitalik and there an "evidence" of his attack. Who will dare to slash him? Vitalik won't include this evidence into "Vitalik's fork". If Vitalik wants to have his own blockchain, nobody cares, isn't it?
There are probably many botnets of IoT devices with 10x that many nodes, aren't there?
So a single botnet could probably ensure that a target victim has the majority of peer connections to the attacker.