Ironic considering that this comment saying comments don't need to be on chain has generated a reward. How much will that reward be worth in 10 years? It absolutely does need to be on chain if it's going to get rewarded. Seeing as the reward period is only 7 days we could be archiving a lot of data off chain once that period is up, in theory. Of course that just creates a new wave of problems in that it becomes much harder to replay a node from the genesis block. There are no one-size-fits all solutions unfortunately.