The fix is really simple. All they need to do is add TextOptions.TextFormattingMode="Display" to every window, and preferably also change the font back to Segoe UI.
Just wanted to follow up on the fonts stuff.
In terms of the "fuzzy" text problem, this is actually subject to personal preference and the technical specifications of your monitor. Many people (myself included) actually don't have any problems with the "current" font rendering. I can agree it's sort
of blurry, but it's readable (better than earlier WPF font rendering) and I actually enjoy the smoother aesthetics. At the same time, I can see why some people can find a problem with it.
In terms of a "solution", it's actually not that straight forward. Scott Hanselman and Pete Brown reached out to me to work on this issue specifically. TextFormattingMode and TextRenderingMode were one of the first things I tried and it really didn't have
any positive effect. To cut a long story short, it actually turns out enabling transparency on the application disables ClearType font rendering application-wide.
We required transparency because of the custom chrome drop shadow we've implemented so currently we need to solve that issue to solve this fonts issue.
Rest assured though, we're looking into this and will seek a solution to satisfy everyone.