The HIVE community controls both HIVE and HIVE-Engine.

Since the HIVE community controls both blockchains, it should be possible to create a trustless transfer mechanism between the two blockchains.

As I understand, every HIVE account has an HE account.

I am not on a HIVE development team. I can imagine several ways of doing this, but I would have to spend time studying the code before suggesting anything.

It is also possible to do swaps without a third party.

I may be wrong but, as I understand, the swap coins on HE are in a wallet held by HIVE Engine.

When a user transfers BTC into HE, the funds transfer into an exchanged owned account. The system references the coins SWAP.BTC on HE.

I could buy the SWAP.BTC and transfer it out. Just as the inbound transaction involved only two wallets, the outbound transaction would involve just the HE wallet and my wallet.

I Am Not Familiar with ThorChain

I am not familiar with ThorChain. I would suspect that many blockchains are looking for ways to integrate their services in a trustless manner.

I suspect that there is a great deal of talent working on the problem. Your linked article mentioned P2PTradeX. I suspect that there are other solutions.

!PIZZA