Take a look at data virtualization. It's an alternative to data warehousing without the burden of making mutiple copies of the data; instead, it retrieves the information fron source systems in real time.
The "single view of customer" use case, which is the one you mention in your post, is one of the oldest that this technology aimed to solve and it does solve it very well.
The "single view of customer" use case, which is the one you mention in your post, is one of the oldest that this technology aimed to solve and it does solve it very well.
Disclaimer: I work for Denodo (http://denodo.com).