But the network/blockchain where the NFT resides is also the most important if you ask me. I believe in 15 - 20 years there will just be 3 to 5 blockchains that exists, and Bitcoin remaining at the center like the Sun of a solar system, still chugging along.
I seriously doubt it. The idea of "penny stocks" is perfected in cryptocurrency world because it is so much easier and cheaper to create altcoins/tokens than it is to start a penny stock and sell it. There is also the benefit of anonymity so things like scams and money laundering will continue happening in altcoin market. Hence we will continue seeing the altcoins grow in number and in 15-20 years we may have more than a million worthless altcoins.