pfSense

Yes, it could live in a column, like the "real" widgets. By default it could go in column 1 above the System Information widget. Users could move it around in just the same way as the "real" widgets to wherever they like in the dashboard columns.
Hmmm - how hard would that be to code?

I get the reason, most won't need it taking up screen space at the top, but it's fine as is too. Maybe just add an option shown when "Available widgets" is expanded to make it go to the bottom of the page instead of the top.

Now there is just a red "+" button on the right-hand side of the breadcrumb bar, before the help "?". That means the Available Widgets section does not take any vertical screen space, unless you want to open it by pressing the "+". Then you can press again to get rid of it any time you like, and it even goes away itself when you click and add any widget.
IMHO the latest UI for this is good, and there is no need for any more on this.

Wow, just noticed what Philip said. This is great now, much better and more clean!