Assume that a centralized altcoin exists that provides useful privacy in areas where it would take more work or be more expensive to achieve comparable privacy on BTC.

If that altcoin was somehow implemented as a privacy layer for BTC (perhaps with atomic swaps) such that you are never exposed to it's volatility or consensus rules. Would you consider using it? Would you still call it an altcoin?

How is this different from something like Liquid or fedimints which also take a privacy vs decentralization tradeoff?