pruning is not the same as a checkpoint which is what Adam proposed. either way it still has to sync entirely as you've mentioned so:
Assuming yearly 20% increase blockchain size & 10% reduction in bandwidth costs, after 15-20 years no new nodes can enter system except maybe huge datacenter operations.
https://www.youtube.com/watch?v=TgjrS-BPWDQ&feature=youtu.be&t=7331Ok, I must have misunderstood.
How would checkpoints work? (I have no clue)
Does this checkpoint basically hold a checksum of all previous transactions confirming that everything up to this point is true. If network has a checkpoint in it's blockchain (the nodes agree upon it) and you start building on it without validating the whole chain before the checkpoint, then what's the problem?