xNote takes another step towards being an OPML outliner. Here's what I added:

• close OPML document
• edit URL
• treeview context menu
• better keyboard support

Some issues that are left:

• I couldn't get the old URL to appear in the Edit Link dialog, working on it
• do we allow newlines in comments?
• do we allow URLs on folders?

... and from before:

• adding nodes
• deleting nodes

Here is the executable (.NET framework required) for your trialing pleasure and the code.