^ I can tell you how L3 would work. (custodial L1/L2 wallets) Global payment processors with deals between them.... except they will probably be using L2/L1 to settle between them regularly (ie: hourly?)
IF Bitcoin some day gets massively adopted, that's how it will be done. You can quote me for posterity.
Yes i can see it happening that way, but what i meant was from a technical point of view how they will achieve this.. so it is trustless and open.