Each person maintains only a couple lightning channels per year, big block:

8B people * 4tx/yr * 250B/tx = 8TB/yr

Each year, a full node would have to add $150 in storage if they only use disks

VS:

Small block, self custody:

8B people * 1tx/person * 10min/2700tx = 56.3yrs

Time to make one transaction per person art current rate.

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There's no way to self-custody for every person at the current rate. As it currently stands, an on-chain transaction will be a once-in-a-lifetime event for 99.99% of people.