How does Nano plan to handle the data growth when the network scales up 10, 100 or 1000 times?
Some of the development was reliant on the Universal Blocks upgrade which was introduced in May 2018 and was being finalized with the release of Epoch blocks. Also, Lazy Boostrapping has now been implemented. These will minimize data growth. That’s one of the strengths with block-lattice architecture. As of Aug 2019, the Nano network has processed near 30 million transactions with an unpruned ledger size of only 15.7GB.
Also, Introducing Ledger Pruning (have the history removed) is a priority for the development team. Accounts with a too low balance can be removed (they can be forced to make the last payment to another account), and pending transactions can be limited per account. For opening new accounts, there is a suggestion to either increase the required PoW (just for opening) or require a minimum deposit to be made to it.