Wired Tiger's storage engine implementation quality is _very_ high. The core developers are experts in the field and really know what they are doing; check the codebase on Github.

Integrating that technology in MongoDB will make a big difference in terms of performance and scalability, and I imagine the folks who built it will be able to put use their skills in good use there, further improving MongoDB left and right. A great deal, of great value, for MongoDB.