Btw, you can do async payments if you open a channel direct with someone using existing tech modified.
Further, check out Hoppr. I'm not telling you to buy it, but look at the tech.
It's an Eth shitcoin, but they use an encryption scheme of revealing to each hop in onion routing the next piece of the puzzle. So if the real reciever, has a direct channel with the last hop of the lightning network, it can use a similar system, to not get access to funds, until it gets the last piece of the puzzle from the real reciever. Which is the same as "you can do async payments if you open a channel direct with someone"
Make sense?