Scaling self custody globally will be near impossible. Second layers can scale transactions but not necessarily custody. If everything can always go back to settle on chain, then the only real self custody solution is scaling the utxo set.
But also I'm just stupid.
If your goal is every human having access to L1 Bitcoin, it's absolutely impossible at current block sizes.
If your goal is the relatively small % that wake up to the need for freedom and are willing to take personal responsibility, I think it's doable but will still be a stretch.
Both situations will likely lead to another blocksize war in the future, especially if you factor in future security issues with reliance on fees alone.
This thread needs more air in the public arena.
There is no chance of scaling self-sovereign BTC usage to a billion people with current tech.
I don't think even channel factories could do it.
On-chain fees are going to be stupidly high when a double digit percentage of the world's economy is bidding for block space. Only institutions will be able to afford to take the risk of opening Lightning channels that could be shut down by someone else.
The banks could probably run Lightning nodes and use e-cash protocols to scale extremely private but custodial BTC to the whole world, but would they play that nice?
Even if they do, this might be better than the current system, but this is not the vision.
I think of that as a problem a couple generations away (not human generations, but Bitcoin epochs). I think first we need to get all the unbanked, banked. Then more people will run lightning nodes (several orders of magnitude more). Then we'll have more ideas and technologies from there, possibly at the wallet level.
But also, I'm stupider.
