Just a quick update, I was busy working on a Power BI presentation and thought let me just download the Microsoft Power BI Designer and see if it has been updated.
And to my great surprise it has. It appears as though it was updated on 21 April 2015.
I then went and installed the downloaded version of Microsoft Power BI Designer.
Upon first look I did not see anything significantly different until I came across this below
As you can see you have the option to click on New Measure, and when you want to create your new measure, it would appear to me that it is using DAX!
And from my previous blog post POWER PIVOT AND DAX IN POWER BI , I know that DAX is already supported in Power BI.
You can download the Power BI Designer update here: Microsoft Power BI Designer