I find myself using custom collections very often lately, since I discovered it's the only way to add an event handler to a container (event handlers for containers could in itself be a feature request). I also have to use them to overcome limitations or bugs in other components, like the default list collection which doesn't yet have Switch press or Icon press event handlers.
As it is now, every time I add a custom collection, I have to wait for it to populate with the default components, only to delete them all after, so I have a clean empty custom collection. This can take several seconds sometimes.
It would be far less anxiety-inducing to be able to simply insert a bare custom collection, or at least be able to choose whether it should be empty or not, similar to how you can create a new empty screen or one from a template (Form screen, Detailed screen, etc.).
Right now, we're basically forced to insert a custom collection that has a template that I basically never need.
I won't even mention being able to save a custom collection as a template (or a pattern), so I can easily reinsert anywhere, without having to hunt for it in various screens and sub-containers to copy and paste elsewhere. That would be just #goals.
What do you think?