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1. An end user will need to be able to transfer BTC to a wallet on a phone and then just use that money across multiple retailers without having to think about it? Paying using NFC or QR codes.
2. Retailers will need to be the ones paying the fees, as they currently do with payment systems. End users don't like paying fees and they are more likely to use fiat as they see a feeless option.
3. It needs to be possible for the user to pay while their device is offline.
Are these 3 things going to be possible with lightning? My understanding is that they won't be and therefore IMO lightning is not the answer.
To my understanding, all of the above should be possible. But it could require trusting 3rd parties, not sure on this.
The "proper" way of using LN would be running a node that is also a hub, connecting to other hubs, opening/closing channels etc. But likely you could outsource this to 3rd party, so you don't have to keep your device online all the time.
So I would imagine something like a lightweight wallet, which allows you to open channel (with zero starting balance) say with Coinbase hub, then you could buy BTC from Coinbase directly on LN (you pay with credit card, they top-up your LN balance) and then you could just transact with any merchant/other users.