It is centralized and same with other altcoins that's being run by a certain company. It would help bitcoin somehow by tagging itself as a 'crypto' because bitcoin is a crypto as well. There will be no ICO but it has a wide range of partnership, yes real partnership so it will have its own usecase. I think this is just another the same stablecoin.
Even if it's a centralised coin it is not a big deal. Why? Crypto market need some big names. It will increase the popularity and more and more people will be aware of the crypto currencies. It is a win - win environment for Cryptocurrency market and big companies.
I also think that the arrival of such companies will help the to the whole market. People who use all the services of the Facebook company are a very large amount of people who will know about cryptocurrencies!