This would require some help from the Parsoid side:

• VE requires knowing the generated HTML for ref bodies, and Parsoid currently only provides these for inline refs with bodies (<ref name=asd>body</ref>), as (data-mw).html.body.
• The simplest way to do this seems to be providing generated HTML for refs inside <references/> as an array of ref bodies inside <references/>'s data-mw.

When I try your sandbox, I can edit the references list using wikitext in the template dialog.

On German Wikipedia, this article is similar but has templates inside <references/>
https://de.wikipedia.org/wiki/This_Is_War?veaction=edit
It isnt editable with this notice repeating many times:

"This reference is defined in a template or other generated block, and for now can only be edited in source mode"

Change 75912 had a related patch set uploaded by Esanders:
[WIP] Ref in references support

https://gerrit.wikimedia.org/r/75912

On Parsoid topfail there are several dewp entries for <!-- comments --> within <references/> being moved around. I couldnt reproduce those bugs, probably because of selective serialization. If this is now editable, these dirty diffs may start happening in production. It would be good to test, but I suspect impact is quite low because I checked 20 featured articles and 10 good articles on dewp, and none had these comments within <references/>.

http://parsoid.wmflabs.org:8001/latestresult/de/Flugplatz_St._Michaelisdonn
http://parsoid.wmflabs.org:8001/latestresult/de/ARO_Heimtextilien

And here is one for whitespace within <references/>

http://parsoid.wmflabs.org:8001/latestresult/de/Trigonias

Change 75912 merged by jenkins-bot:
Ref in references support

https://gerrit.wikimedia.org/r/75912

This is now merged and will get deployed today; however, to actually do what people want depends on a change in Parsoid that will get deployed tomorrow.