Currently, if I go to https://www.mediawiki.org/wiki/User:Amire80/ve-poem and edit it using VE, I can edit the content of the <poem> tag. If my UI language is Hebrew, then the <textarea> for editing the poem is RTL. I would expect it to be LTR.
Ideally the default direction for the <textarea> that this feature should be the direction of the surrounding text. If it's hard to get, then the direction of the page's content will probably suffice. (Currently it will be the same as the content language of the wiki, but it may change some day when we finally introduce page language.)
There can also be some tags for which the default direction must be different, such as <source>, but that's an issue for a separate bug.