Interestingly Bart said in the video above:
Currently I'm working in the Online Services Division, but my big passions are actually virtual machines and languages, I leave it to your imagination what I'm working on in Online Services.
My guess is something similiar to Tangram:
The technology stack includes a declarative side-effect free runtime, an expression language, a graph-based document architecture, and an authoring environment. The technology is shipping as part of Microsoft Powerview, and has been live in Bing since 2009.
Just a thought , of course there are many other stuff like Cosmos/Scope, or something completely new.