There are some Proof-Of-Work chains where pruning is default on their nodes, i.e. the network does not rely on full unpruned nodes at all:

Due to the pruning mechanism, Kaspa nodes only needs ~3 days of prior history to be stored by each decentralized machine.

1. Do Kaspa rely on additional assumptions that Bitcoin do not rely on in order for such prunning to work?

2. How do Kaspa nodes construct their utxo set in such circumstances?

Who is to verify the signature

Lets imagine that some time in the future due to some reason (be it high cost of storage or due to protest against on-chain inscriptions) everybody node on a Bitcoin network is a pruned node. In that circumstances and within current Bitcoin protocol:

3. Would it be possible to start a new node from scratch. Would it possible to verify a the last 550 mb of blocks without having a connection with even one full, archival node.

4. With a node that was just started from scratch, would it be possible for such a node to construct the UTXO set in which there would be some utxos that were created below the blockheight of the chop off point. As far as I know, the utxo set is constructed by each node based on the data in the blocks (and not synced with other nodes as it is the case with blocks) – correct me if I am wrong.