I have not been able to find any information since Opera's original announcement 5 months ago that "Opera Mini will become the default web browser for Microsoft’s existing feature phones and Asha phones portfolio" (http://www.operasoftware.com/press/releases/mobile/2014-08-21)

This process has already started (see, for example, http://blogs.opera.com/mobile/2015/01/microsofts-affordable-phone-comes-preinstalled-opera-mini/ and http://www.microsoft.com/en-au/mobile/support/product/nokia-xpress-asha/faq/?action=singleTopic&topic=FA144249&category=).

At the moment, there are some really significant things that Nokia Xpress does better than Opera Mini 8, as well as lots of things that Opera Mini does better, and some of these should be easy to fix in, say, version 8.2 without needing to wait for more details in a version 9.

For example, it is possible to make a phone call, move the phone to silent mode, or start/stop music on my phone when using Nokia Xpress, whereas Opera Mini needs to be closed completely. This really reduces the usability of the smartphone.