Avaible size based DataTemplate selection

It would be more then useful to be able to define a datatemplate depending on the avaible size, as in somecases the Region on which we want to display data can Change dramaticly.
If we could do something like this:

```













```
This would leave the current behaviour more or less intakt but would make it possible to make a more resiliant UI where I can use the place that I have quite optimal.