It'll be difficult to onboard billions of people without some sort of channel factory, either through eltoo, or more interestingly a recent proposal by John Law to add hierarchical channels without a soft-fork (https://github.com/JohnLaw2/ln-hierarchical-channels/blob/main/hierarchicalchannels12.pdf) which would allow more users to be added to channels off-chain, and liquidity to be rebalanced in these hierarchical channels off-chain. Essentially this proposal is to Lightning what Lightning is to Bitcoin, allowing more things to be done off-chain.

Second concern is channel jamming, and as far as I know there is no "good" solution to this yet. When you make a LN payment, liquidity is locked up along the route until the payment is settled. But researchers have shown channel jamming attacks to be possible, where a malicious user can refuse to settle the payment, causing liquidity to be locked up for potentially hours/days, and even trigger force-closes of channels.

As far as I know there is no good solution to the second problem yet. There are experiments of adding a "reputation score" to lightning nodes, and thus lightning nodes could limit the amount of liquidity they lock up for untrusted nodes, but this would lead to several issues. First this would lead to a somewhat worse experience for new users, because they might not be able to make moderately-sized payments until their score goes up, pushing them to centralized alternatives. Second, it's not clear if this would even work, a malicious attacker could slowly accumulate reputation and then execute the attack.