In order for the average Joe to create off-chain transactions, he has to open two on-chain ones except if he's under the control of another party. But then, isn't the whole system ruined? 
Unfortunately I do expect that the channels will be opened between custodians. Indeed, not a great future for Bitcoin-as-a-currency, I know that too.
But, the security will decrease a lot sooner than that. Sure, in 100 years each block will reward 32 sats, but what will happen once Bitcoin reaches $10-100 trillion market cap and suddenly the reward of the network cuts in half? Will the security drop by half or will the market cap double?
It's sort of a dead end.
It's sort of a dead end.
He-heh.. I've been thinking on such scenarios in the past and sooner or later all led to dead-ends or things we just cannot foresee. So I've stopped worrying and making scenarios.