If Facebook is really building a blockchain, then I think that they are already digging their grave already, except maybe they will regulate the blockchain and any project that will want to come through their chain, because we can see what is happening to Ethereum right now.
If they dont regulate their blockchain, there are going to be lots of shit projects for sure. But, the way Im seeing it they are going to be regulating their blockchain. Facebook is a big company and I dont think they would like any of such things staining their name. Because, if they allow such things to happen then its going to make a lot of people hate them for it and that is going to cause them a bad business, which Im very sure they wouldnt like of course. But, we cant tell the future, its still a long way ahead
so till then we will get to know the full plans they have for this their Libra.
Whatever blockchain that Facebook is building will be very similar to the services of Ethereum also and if that is the case, they will surely affect the existence of Ethereum
But, this is not the future I want. Libra is a stable coin and I want it to be a future on stablecoin industry and not into smart contract areas. Dual functionalities may lead to misunderstanding of application of libra which is more dangerous one as it directly affects new adopters.