A couple counter-points:

> assuming wallet infrastructure

> the *recipient* now pays fees

The sender could be the one responsible for getting txs confirmed (CPFPing as needed), which simplifies things a bunch.

You don't really need specialized wallet support in this case, you could just send txs by email (for emergency if the sender doesn't confirm them, typically not used) and have users verify inclusion with some external website/tool.

Given that senders are expected to be exchanges and the like, it seems plausible that users could mostly rely on them to get txs confirmed and wouldn't mind waiting for it to show up. (as long as they have a backup)

Admittedly this does get quite a bit more complicated if the receiver is responsible for fees.

> You don't want your funds stuck on chain. Many might want theirs transferred in one tx to Coinbase.

A cool thing about congestion control is that if the recipient is a custodian with sufficient liquidity, they could credit their customers immediately.

So basically if you withdraw from one exchange into another and provide them with a payment inclusion proof, you won't actually have to wait for it to unroll for it to show up in your balance.