I think every node needs the same dataset for the blockchain to be valid.
Maybe a rolling dataset, with the earliest transactions falling off after their data is somehow archived (but accessible to the current nodes)?
OR
The current nodes could do a hardfork (NewNodes), with the ability to reference the legacy chain snapshot for the next X years.
Wallet1 created in 2015. Contains 1 XMR. Hardfork in 2025 to truncate the entire DB which becomes a balance reference copy. After the snapshot, they would have a balance on the "new" chain. In order to transact, they'd have to use a New Node which knows their previous balance from the legacy chain.
Is that possible?