100 mil would be equivalent to nearly 2000 trillion market cap for bitcoin alone. For this to be possible, the dollar would have to be worth next to nothing. What good is a 100 million bitcoin if it takes 1 million to buy a loaf of bread? At some point these comparisons break down to meaninglessness.

This kind of dominance of a single crypto is unlikely. We are much more likely to have a few dozen coins all with relatively similar market cap. There's a name for everyone under one umbrella: it's called centralization.