Speaking in what's out there now, there is Nano that only requires latest data (latest block) to participate in consensus (called a Current Node). I know that d

Speaking in what's out there now, there is Nano that only requires latest data (latest block) to participate in consensus (called a Current Node). I know that doesn't answer your more broad question of if its necessary but thought I'd point that out. It would mean that nodes can store only some of the ledger. Even in the case of a node storing historical data not directly connected to the current block, such a node would only need to get the last block (and not the in-between ones) in order to jump back into consensus (someone please correct me if I'm wrong on this).