I've taken the liberty of changing the category to "Link Handling & Routing" and the priority to "Could have".

This should IMHO be seen as a feature request to add this capability at a much lower level: in TypoLink itself. As you mention in the criteria, it should be possible for an editor to configure this and that means it should be part of the regular link creation when you target files, and that the attribute should be added when cObj->typoLink creates a tag.

After that is then added it may be necessary to adapt one or two ViewHelpers, specifically those that create the href with typoLink but the tag with Fluid's AbstractTagBasedViewHelper parent class.

NB: It may even be possible to somehow configure typoLink default behaviors to add this attribute; just mentioning that to say it might be possible for you to get this behavior by customising TS a bit and using typoLink whenever you can (it can also create links to FAL files, just use the t3://file?uid=123 format of link)