Pesonally, I am still struggling to see where PowerBI fits in my organization. I am the only BI professional here, so I have to do every bit of the process from data modeling to building front end applications. Right now, my organization has a data warehouse with some processes in the warehouse, a Datazen environment and an SSRS environment. There is no SSAS cubes or any power users using PowerPivot to analyze data.
Data warehouses serve a particular role in an environment: they answer known business questions and give consistent answers across an organization. I see Power BI as a tool with a few separate uses depending upon organizational size and maturity. I think its best use in shops which are not large enough, well-established enough, or with enough non-IT business intelligence expertise is BI developers building beautiful dashboards for business data consumers, feeding from existing systems (including data warehouses). In that sense, it is a complement to a Kimball-style data warehouse.