There's two distinct concepts that are often confused: atomic swaps and trustless crosschain transfers. 

Atomic swap technology is well-established and relatively simple to implement (it was implemented in BitShares for instance). You can find more about the tech [here](https://en.bitcoin.it/wiki/Hash_Time_Locked_Contracts). But as the BitShares guys found (well, I tried to tell them before they implemented it), it's not really the technology they were looking for.

What people are usually looking for is a trustless way to transfer a coin back and forth between blockchain networks. Atomic  swaps don't achieve this, because they don't provide a mechanism to peg the value between coins on each network. 

Trustless crosschain transfer is a much more difficult problem, although there are feasible solutions. We did some research into this area many years ago and had what I believe were viable ideas for it, and it is quite likely we might revisit the ideas again. But it's not something I'm planning for hardfork 25.