Tags are a major part of the iOS app. Adding them to the online outline page would be beneficial.

At present when an outline is saved from Outliner Online, once reloaded frequently all nodes are in an expanded state. While they can be collapsed manually and that state seems to stick, using "collapse all" doesn't seem to stick at all.

On some of my outlines, I like to know how many children are below a given item. For example, a list of blog post ideas could be grouped under "Future", "Draft", and "Published" items. It would be nice to have the option to show how many children (but not grandchildren or great-grandchildren, etc..) are in each category.

I'd love any easy way to stamp (type) in the current date & time.

That and be able to see a per-item timestamp on an element in the outline. I suppose this would lead to having both a created and a modified timestamp.

But a quick timestamp macro would be great in the meantime.

The web version is too small and not practical to use on an Android phone. Can you either make an Android App or make a mobile version of the website that adjusts to the users device.
There are now more Android users in the world than iOS. Please take our money.

Mindmap / PDF / Markdown ...

An autosave feature

If you have more than a few outlines, you'll really need to group them into folders. CarbonFin Outliner doesn't currently support folders in Dropbox.

So the storage location defaults to Dropbox.

It would be nice if one could add priorities to tasks and sort tasks by priority.

Add a radio button to options, or modify Archive, to protect an outline from being inadvertently deleted. This happened to me when I was trying to deconflict a file on my iPad with one on my iPhone. I inadvertently swiped a similarly named outline and the sync process deleted it instantly on both devices with no way for me to undo that deletion. I lost an outline representing the entirety of my work in the month of June! With a protect mode, it would at least give me a question for verification.