In a certain way, one could say that Monero has already replaced bitcoin in its original conception, namely as an anarchist currency. Bitcoin has, unfortenately, become an half-institutionalized gambling/speculating tool with more and more demand for state justice, legal interference, and "mainstream regulation". Most of the market cap of bitcoin is made of speculation as just another financial tool in the big toolbox of financial gamblers, and only a minuscule tiny fraction is devoted to the original goal of bitcoin, which was freedom from state, law and finance. Monero still has most of that promise, as I don't think that its market cap is mainly driven by financial gamblers. However, it is true that monero is, as far as I know, not (yet ?) used as a genuine currency, as bitcoin was at a certain point, on the dark net.