Add a password recovery feature for administrators who forget their passwords.
Mango does not store the actual passwords, so link sent to admin email will require him/her to reset it.

Add support for enclosures. This will include a place to add the enclosures in the admin post form and a set of tags to show it in the themes.

Implement automatic notification by email to plugin developers when an untrapped error occurs with their plugin (i.e. one that's logged in Mango's error logs). Blog owners should have the ability to opt out of this reporting.

This could be useful in a temporary situation like moving from one server to another, where you want to leave the blog running on the old box while DNS changes propagate and point people to the new box, where comments are enabled.

Currently you can disable comments on a per-post/page basis, but it would be nice to have a single global override.

The new post/page revision history feature is great. However, I find myself making lots of small changes to posts, which can quickly add up to quite a lengthy history!

For instance, I wrote a post today, and just in the process of fine-tuning and publishing it, I racked up 17 revisions!

I propose the ability to remove individual items from the revision history.

On the add/edit post/page forms, should be as simple as moving the event broadcast to before the custom fields section.

My estimation (guess) is that far more people use custom generated content on this page (i.e. related entries) than the custom fields block. Heck, I wouldn't mind an option/setting to hide those fields altogether.