So in summary, to my earlier question about Lightning scalability:

Using back of the napkin calculations, you probably couldn’t onboard 1 billion users to Lightning within a 5 year period because each new user requires an on chain transaction to open a new channel and it would take Bitcoin 5 years to process those transactions.

But there are possible future solutions that could reduce the number/size of onchain transactions to onboard users, or a different blockchain-based layer 2 could be used with bigger blocks which Lightning rides on top of as layer 3 which would allow a greater capacity for new user onboarding.