What do you mean by "100% mass adoption"?
I'm not even sure what the term
adoption means, much less 100%. Does adoption mean someone is using bitcoin as a substitute for fiat? Does it mean they're using it as an investment? Is it that they just own some for whatever reason?
People are generally not using bitcoin to buy things with, though there are certainly a small number of them doing so. And I don't think bitcoin is ever going to get to a point where it starts to replace fiat currencies unless something seriously goes wrong with every single fiat currency in the world such that they become worthless. That could happen to a handful of them simultaneously, but it's doubtful it'll happen globally. So I'm comfortable ruling that out entirely.
If mass adoption means most people own bitcoin and hold it as an investment (or use it to buy things), I'm guessing the number is somewhere between 1-5%, maybe more. Most people I know IRL are aware of bitcoin but don't own any, so an estimate of 5/100 people owning it sounds about right to me. It's hard to tell, because bitcoin doesn't come up in conversation a lot (for me), plus people don't tend to advertise the fact that they own it, so it's difficult to estimate.
The bottom line though is that we're still nowhere near mass adoption, no matter how you define that term.