In my opinion, I think it's possible considering the fact that we only have about 7 to 11 crypto users presently and adoption rate is still minimal. With mainstream adoption, then $20 should be possible. This is just my opinion, please feel free to share yours?
Can we reach a $20 trillion market cap by 2028 ?
It would actually take much more than a 20 fold increase from now. As the market capitalization is under $300 billion at the moment across the entire crypto board, it makes more sense to say a 50-60 times fold.
It's definitely possible, though, considering that adoption is going to continue to climb in the next decade. And if previous growth cycles can sustain, there would be no question that it can happen. We've seen a 2000% increase in price from start of last year to end of last year alone, albeit the dump. Furthermore, the inflation of fiat would be a catalyst as well.
A variety of things could happen that would hinder the growth of price though, including a delayed mass adoption. It could happen, but it's not 100% going to happen, since $20 trillion would represent a pretty big fraction of even the entire money supply in physical banknotes and coins.