I don't think Bitcoin will "go out of fashion." In the long run, I believe it will "flip" the market cap of gold and become the new standard hedge against inflation. I've read reports that Bitcoin mining is already being used to subsidize green energy infrastructure. If this trend continues, then its role in making the transition from fossil fuels more economical will outweigh any temporary setbacks it has caused via increased energy consumption.

I'm still not really up-to-date on Lightning Network and its potential. But even without that, I think that Bitcoin will remain dominant in the cryptocurrency space due to network effects. It has the best name recognition, the most secure PoW blockchain, and the highest capitalization. Ethereum will likely stay quite relevant, but between its migration to the less-secure PoS system, and its constant inflation rate without any cap (vs. Bitcoin's decreasing one with the 21 million cap), I think that Bitcoin will continue to be prized as a store of value.