Agree, I've worked on the "decentralization" process for Hive-Engine, they just haven't deployed it yet (although in its current form, anyone can run a Hive-Engine node, there's just no incentive to do so, only SCOT and STEEM/HIVE pegged tokens are fully centralized).
But yes, I'd rather have atomic swaps fully integrated in the Hive core software as well. (and a second layer engine could be used for other "types of tokens" that Hive will never handle directly. (NFTs for example))