Add support for Redactor RTE
Though I have never used this, I believe from everything I have read on it, that it would be a major upgrade over TinyMCE and fckEditor. I believe the admin speed would also increase as the total weight of the editor is only 45kb. The features I would like to personally see implemented as a part of this:
Ability to customize what controls are presented when an editor is loaded. Example: most of the time, I don't want me clients to have the ability to change font color, change font sizes, adjust justification, etc. I want them to have RTE for bold, italic, adding images, links, and adjust between headers/paragraphs/blockquotes. I believe adding this, with setting up site-wide settings and allowing overrides (for app RTE attributes, page content layouts, etc.).
This would also allow click-to-edit ability: http://imperavi.com/redactor/examples/click-to-edit/ or even the air mode: http://imperavi.com/redactor/examples/air/http://imperavi.com/redactor/examples/click-to-edit/http://imperavi.com/redactor/examples/air/
It also has built in auto save functionality and supports HTML5.
Finally, this works iOS and Android 4 so editing the site on tablets and phones would be possible.
Customer support service by UserEcho
I'm not sure I follow your concern on the file/image browser. It seems to have that support built in. On the home page it shows that example. You can also create custom buttons with this, so you could actually use the same dialog that you currently use as an image/file upload attribute type as a button in the RTE.
My biggest concern with this RTE is it's lack of a file/image browser. That is a critical feature for just about any content editor.
With that said, it seems like an interesting editor and I do like that it's mobile friendly. TinyMCE is mobile friendly for newer mobile devices running the latest browser versions.
I also agree with you that it would also be useful to be able to configure which buttons show in TinyMCE.