Time for Some Improved Structuring of XAML
When programming languages began they where structured well enough to deal with the complexities of applications at the time. Then as apps got more sophisticated the existing languages became overwhelmed by the complexity. Thus assembly language programming changed to C which changed to C++ and now to C#. Each of these steps "cleaned up" the mess layered on top of the prior language to help it deal with more sophisticated apps.
XAML has been great, but it's been taking on more and more burden. In response, an improved ability to structure XAML better is needed. Ways to break down huge XAML files into smaller, likely reusable, components.
With the introduction of more and more "fancy" to XAML (animation, depth, etc), being able to break down an ever-increasing size XAML page file into more manageable sub-files is becoming increasingly critical. The next step is introducing "XAML macro" files where the reference to a XAML macro file can include parameters that get substituted into the merged XAML as the referenced file is merged at compiler time.