By 2040, I suspect I will be able to phase out credit cards entirely, and pay for all of my expenses directly with #Bitcoin, even in somewhere as developed as the United States.

This implies (A) vendors and businesses adopt #Bitcoin receivable tech in mass [lightning], (B) that privacy preserving tech like Ark has matured enough to be used in every day real life, and (C) legislative bodies have cleared out impediments to using #Bitcoin as money.

It's a lot of stars to align, but I think that's a reasonable expectation and a reasonable timeline.