$1m is absurdly unrealistic. If that happens then the demand of Bitcoin is superb that all other altcoins is neglected. Nowadays crypto competitions is high and it is difficult to reach that certain amount you said.
Around a few years back people were thinking that bitcoin never reaches 10K and it will be unrealistic. But bitcoin has surprised everyone in just last one year it went up to 20K. This market is not controlled by any institution or government so anything can happen either it can reach to 1 Million or similarly it can go down as well. As a crypto investor, we should be always ready to receive surprises from this market.
Well expecting surprises might be a good thing but being optimistic all the time calls for being realistic as well. If the value of bitcoin reaches $1 million dollars, the demand for such cryptocurrency would be high and its supply might decrease. Not to mention with that value being that significantly high, investors would actually pull out their investments due to the risk and threat of its value dropping. Its decentralized and high-volatile nature make bitcoin as 'high-risk, high-reward' type of investment wherein you are holding a double-edged sword on your part.
Assuming that bitcoin would be regulated in the future and its value would be less-volatile, the number of investors might pull-out their investments. What makes bitcoin as an opportunity to most investors is its volatile price. Some consider this as a short to mid-term investment since its price may skyrocket at any time- which makes this the perfect tool for risk takers.