Lightning is not easy for Merchants. And frankly... I think they should be using custodial solutions to start, unless they are really really committed.

As far as self custody and Lightning goes...

I was able to use Lightning across continents from my own node (LND) and I am not a heavy command-line user. Granted there wasn't anyone else paying in Bitcoin in Lugano (not many people) but at least it worked.

I have set up a self-contained 'zeus' node on a phone too and it's as easy as... zapping the Lightning channel the LSP is setting up for you.

Then you have a channel you've 'rented' and you can send sats to it. Few if any on-chain fees and you can swap out into cold storage whenever you want. What's the issue with this?

In my opinion it's not a technical challenge, but an educational one. Just my opinion.