For non-technical holders of BTC (i.e. the mass of the BTC population), the risk of inanonymity and centralisation still there: as they have to entirely rely on their wallet providers? If such wallet providers are hacked or meddled with their users, the users won't have anyway to protect themselves or anyone to make a claim on? Their fund in BTC is entire at the mercy of the wallets?
If you control your own private keys, you don't need to worry about what happens to wallet providers. I assume you're talking about web wallet providers like Xapo and Coinbase, right? Then indeed, they can be hacked and you could lose everything. It's much safer to download a local desktop wallet like Core (or Electrum for a lightweight wallet) that gives you control over your coins.
How you think BTC would work for the ordinary people in the future to replace their current existing financial assets and management with fiat currencies?
I think BTC for day-to-day purchasing will function much like Venmo and similar apps. It will likely be powered by the Lightning Network, and users will largely not understand how it works. But I don't think BTC will ever replace fiat currencies. That would only happen if governments themselves disappeared entirely.