I imagine something like a hybrid of InterPlanetary file system and Ethereum blockchain, where you pay a fee to upload a file that is then kept safe for 120 years in a distributed filesystem. Basically a lifetime insurance policy for your data.
You would store your most important photos, video clips, favorite songs, books, quotes, pieces of wisdom, whatever piece of data you want to keep forever.
The upload fee guarantees 120 years of safe storage and is distributed over time to people who host the nodes/files on their networks.
The fee calculation is based on an algorithm that takes into account various parameters such as future energy and hardware price projections, etc.
The files can only be accessed if you know the 24-word seed phrase (elaborate password). Memorize the words, tattoo them on your body, carve them in stone, engrave them somewhere - whatever you need to do to keep them forever.
People would be incentivized to keep the nodes going because 120 years worth of payment is already deposited. The market would determine the size of the network. The more there are file uploaders, the more there would be nodes.
The encrypted data would spread over the entire network so that every bit is kept safe even if half the network goes down. There could be several libraries that keep the entire blockchain history on disks in warehouses - for recovery if something goes catastrophically wrong.
To protect the file hosting nodes from excessive bandwidth use there could be a micro fee per download.