Bitcoin is outdated, slow, and expensive. Ethereum is the foundation for all ERC20 tokens, getting closer to POS implementation, which will further improve scalability, cost, and speed of the network. All these are solid fundamentals for Ethereum market cap to exceed that of Bitcoin's.
The magic number of 0.1732 is when Ethereum will be more expensive than Bitcoin in market cap. This moment was labeled as "the flippening" in the crypto community. Here is a potential scenario.