500 times per second? That must be far into the future.
What do you mean by one action done because of another?
If you but a pixel in this "place", you do it because you've lost, you don't want to buy it for free. You need to be 100% sure a specific action happened and this can't be done with
"you do it because you've lost, you don't want to buy it for free" -> because you've lost it, and don't want to buy it if you already have it. So it depends if someone just bought it
a blockchain (this is why Hashgraph claim to be "safe") But I've not read satoshis.place code so I might be wrong and it might be slow enough to be be done on a blockchain