If I had a magic wand I would change this:

When I do Drag & Drop, it appears this popup:

Now, whatever is the destination of the above link (so I mean - with or without T15165) me and some of my friends find it extremely irritating that the work on the current screen is abandoned by default, since it does not open in a new tab as default.

About External Link in General

Note that most web designers hate external links for a reason, and I totally agree with them. This is an interesting discussion:

https://stackoverflow.com/q/946248

Notes:

• https://stackoverflow.com/a/946263 - I agree with Reed Copsey who says that external links are usually annoying in normal navigation (comment respected, since this is not a "normal navigation" at all, but an interactive editing mode)
• https://stackoverflow.com/a/946282 - I also totally agree with user John MacIntyre who says «The current form may be in edit mode, and you want to be able to open another page without either disregarding or saving the current one.»
• https://stackoverflow.com/a/946273/3451846 - I also agree with Gabriel Hurley: «It lets them leave your site without losing their place on your page or have to use the back button.» - the back sometime cannot do miracles and cannot recover your edited post

We know this deserves a little of introspection.

• Case: humans are curious - we see a thing, we want to click on things, without losing their work
  • → 🔴 this is probably not a case to be recommended. Don't randomly click things at home. Don't touch everything sparkling. Accept popups only from people you know. Phorge should not try to protect you from this bad web assumption.
• Case: people want to close the popup but whooooopsy with my mouse I've accidentally opened the link in the popup and not the popup itself, so I technically opened a link and that is why I've lost my work - that link should be an external link1!1!
  • → 🔴 this is also not a good use-case. Users must to think twice before using their mouse or similar powerful accurate technologies. With great power comes great responsibility.
• Case: people want to close the popup but whooooopsy with my finger I've accidentally opened the link in the popup and not the popup itself, so I technically opened a link and that is why I've lost my work - that link should be an external link1!1!
  • → 🔴 a mobile accessibility issue should not be handled with an external link but with bigger links and bigger buttons, so whenever you have an inaccurate touch screen or just a fat finger, your actions are safe. Anyway, if your finger is really fat you will probably have problems in many other applications. We are really sorry for this accessibility issue. But, a mitigation for this personal issue is to adopt a mouse, instead of a touch device. Try that. Mouses are awesome.
• Case: people want to visit the File page to: change the Visibility permissions, set a nice title, leave a comment like "Wow, nice File" or whatever and then being able to turn back to their work
  • → 🟢 Yes. It makes sense to assume that the majority of the people just want to be able to visit the File page after a Drag & Drop, and then be able to turn back, as default, without any risk of losing their form.data. This is why it makes sense to put an external link in that popup.
• Case: the user has a modal opened, changing stuff, and the user supposes that the modal is strong enough to don't lose changes (after T15034: Show confirmation dialog when closing a modal if form contents have been changed) but, the user does a Drag & Drop, clicks on the Popup link for some reasons, and puff, the confirmation dialog is not shown, and the link is opened in the same tab, losing the work of the user.
  • → 🟢 The fact that Dialog currently does not prevent this kind of opening somehow supports the need for an external link here.
• Case: Take the above case, but suppose that the Dialog now could prevent normal links - for example thanks to a future patch that listens to the onblur event or something like that and shows a confirmation dialog also for that case.
  • → 🟢 In that case, the user who wants to click on the link to the File, still wants to visit the link to the File, and does not want to see a confirmation dialog, where they must choose: "do you lose your work visiting the link, or do you do nothing (without visiting the link)?". So this still gives much sense to adopt an external link. So the current and future situation of the confirmation dialog does not affect the need of an external link here.

About this specific External Link

In short, in this specific case is reasonable to have external link.

This Task should not pave the way for using external links indiscriminately.