Also, what do you think are the chances that it could happen? I would like to hear your thoughts and opinions.
In my own opinion, the case where altcoins like ETH surpassing the BTC in terms of value is POSSIBLE but not PROBABLE. I mean, it is really possible that it will happen, but the probability is less than 1%, I think. Bitcoin was the first cryptocurrency in the world, and it is hard for people to just leave bitcoin and transfer their money to other altoins (I mean, why should I choose those new cryptos and leave the TRUSTED, TRIED, and TESTED).
What will you do if some altcoin (XMR or ETH for example surpasses the value of BTC, either in market cap or by the price of a token each? Will you sell your BTC to buy the more "valuable" coin, or continue using and holding BTC?
If ever any altcoins surpasses BTC in terms of its value and market cap, then I would still hold on my BTC. Why will I buy these altcoins AFTER surpassing BTC? That will be an unwise decision. The thing here is that we should buy the cheaper altcoins/tokens and wait for their values to rise up, not to buy altcoins/tokens with high value.