global/directory namespace usage declaration

[emphasis87]

Would it be possible to have something akin to C# global using declarations? Either global or applied to descendants in a directory.

It quickly gets cumbersome to have custom namespace declarations in all components in the project.
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

There could be other default values, like
mc:Ignorable="d"

which would be nice to declare only once per project/directory.