The answer is reasonably simple - a globally-agreed-upon time-ordered database can act as an anti-cheating layer for new protocols built on top of it. Lightning

The answer is reasonably simple - a globally-agreed-upon time-ordered database can act as an anti-cheating layer for new protocols built on top of it. Lightning Network is a simplistic option, and I reckon there'll be more over time. These protocols may allow nodes to only watch transactions that they're interested in, and participate in a blockchain only indirectly - storing or even hearing about the whole chain becomes unnecessary for most nodes. I do hope that proof-of-stake or a similar system come into being trustworthy systems, however, to decouple the security of a blockchain from its energy usage.