it is not going to happen unless you stop calling market cap dominance
otherwise as long as people use market cap as dominance and as long as it is super easy to create billions of shitcoins by clicking a button then bitcoin's dominance will continue to go down. by 2020 at least we will see 10000 altcoins with a total supply of probably around a thousand-trillion and bitcoin even with its price at $1 million won't even be able to have a market cap to compete with that much supply.
Is this true? I mean, I heard similar explanations before but I always doubted them. If it was so easy to create a sh*tcoin with whichever marketcap you want, why we never see any of them in the top 20 on CoinMarketCap? I'm not sure if I'm right, but I think that it's not that easy for your coin to be even listed on CoinMarketCap.
For example, when you want to add a coin you have to answer the question:
Is the cryptocurrency currently traded on at least 2 exchanges listed on CoinMarketCap.com?
And if the answer is No, then your coin will not be even considered for adding.