RE: Sustainability in Crypto

Very good observations and yes, that's the premises from which blockchains start. That there will be evolutions both at the software and at the hardware level to make it sustainable for a longer period.

Keeping the base layer light and moving more and more on the 2nd layers and sidechains will also help.

There was a discussion on the former chain to prune the blockchain. The decision was to not go ahead with it at that time, but the time may come when such a decision may be on the table again.