T E,
I was intrigued and planned to have something similar for some time. This includes edit in new window/or modal. The open in new window has a fix in the pre-release so I experimented with a copy. By using the edit template I have it working but some small artifacts that need work, for example this is how it opened,

I have to click near the down arrows to make the edit content appear;

Modal's require multiple tiddlers and fields set so its not trivial to share the code patterns.
Edit in new window looks better but I need to resolve the focus issue

Please ask if you want me to share my buggy and unfinished code.
Remember that normally editing a tiddler that the edit methods rename it to a draft tiddler, thus I have excluded title from this example, however the tag and type can be edited the field editor throws some bugs.
I think edit in modal is good for keeping edit restricted to one tiddler at a time for novices and could "replace" the normal edit button in some implementations. Modifying the modal size may need a hack.
The open in new window could allow multiple tiddlers open for edit, and easily can be made full screen.
Regards
Tony