[uncletammy]

I think this is depends on how large the network has scaled at the time the block reward dies. If BTC is doing 100x visa levels, each transaction fee can have a tiny fee and mining would still be viable.

That being said, I don't BTC has any intention of scaling to that degree (or at all really). The BTC devs seem much more concerned with building second layer products like lightning network. All these products actually reduce the number of on-chain transactions and by extension, miner revenue.

[imtringued]

The problem is that lightning is basically federated Paypal. You have to trust your specific provider to some degree. If he stiffs you, you can get arbitration on-chain. There are almost zero barriers to entry so Paypal can be replaced by Paypal 2.0.

I don't believe for one second that when you increase the size of the audience that anyone will care which provider they use. In practice that means they will just use Visa, Mastercard and Paypal, maybe even by skipping lightning entirely.