Extend core textarea / text block email dialog


I’m facing a problem, or rather a dead end, with the textarea or text block email dialog. I’ve done my fair share of querying but simply couldn’t find a solution.

My goal is to have have a subject field (and more generally; any email related fields) be editable directly and intuitively from the email dialog. I have only found this rather lovely plugin by Moritz Ebeling which unfortunately misses this specific functionality.

Ideally, this dialog would have an extra subject field that would either output something like (email: xxx@xxx.com text: yyy subject: zzz) for a textarea field or, for the text block, an anchor with mailto:xxx@xxx.com?subject=zzz as an href attribute.

Please let me know if such method would be possible,
Have a pleasant day,
Noé Gogniat <3