Having a centralized currency is a reasonable thing, though the Fed is a private entity, it operates ultimately like other central banks.
The banks don't have any special power - if you want to open one, you can do that right now.
If they did have some special sauce, VC would be pouring it, and mostly, it's not.
Banks don't make their money or derive their power through the 'creation of money'.
FB's move into this arena is possibly more destabilizing than anything, hopefully, the opportunities will outweigh the risks.