No, you should use proper abstractions to allow you to "easily" replace components down the road. There's no point in planning, designing, or building your application for a million users because by the time you get there: 1 - the business needs will be radically different from what you expected initially, and 2 - you'll have dozens more engineers who will probably do the actual work. It's exceedingly unlikely that the architecture decisions that you made will be relevant at that time.

Also, the overwhelming majority of companies that claim that they need to scale into the millions of DAU will never make it there.