No official announcement has been made about MP6 yet, so how do know that it's the future of the WordPress admin area?

First, MP6 was on the roadmap for WordPress 3.6 before being pushed back. Some of the people most involved in core development are now raising the idea of including MP6 in WordPress 3.7:

Matt Thomas said, "we’re currently aiming for 3.7 but that’s not official yet."

Jen Mylo commented that, "in 3.7 that icon style will be replaced by the icon style in MP6, so it will likely have a pretty different feel".

It's possible that some or all of MP6 may not be included in 3.7, but it is highly likely to be adopted in future releases.

Second, Matt Mullenweg is part of the MP6 developer team.

Third, MP6 looks exactly like the new WordPress.org design. Here's a sneak peak of the new MP6 admin area: