It'll be a fine day when we can swap around coins A and B, from chain A and B. I know there are swapping doohickeys now like Uniswap (never used it), but as I understand, they all require some sort of wrapped token. Yes?
The goal is to get things from A to B without either having to (a) go to a centralized exchange or (b) if dealing person-to-person, rely on trust that the other person will indeed carry through with their end of the bargain.
In the illustration above, I suppose there should be some sort of a fallback. If person with Crypto B doesn't fulfill their obligation, the 20 A reverts back to Crypto A's wallet. The deal just doesn't go through, but there's no change...started 100Acoin & 10 Bcoin, and ended that way.
And on that topic, Thorchain is to go live today: https://www.coindesk.com/thorchain-launch-trustless-cross-chain-crypto-trading
I've not heard much about it, but I love the concept. We'll see how things go.