Thanks everyone for all the info, pointers and comments!
@Subbu: Indeed that was the one I read about, thanks!
@Thiemo: What I'm thinking of is a
gadget, so it would be available on Wikimedia wikis (and any other) but only for users that choose to enable it (similar to my gadget
MiniEdit).
The gadget would allow its users to highlight some text and publish a comment to the talk page along with the highlighted text and parent paragraph (for context). Like so:
In ancient times, the use of solar energy was believed to have existed in civilizations amidst the Greeks, Romans and the Chinese, though not for cooking.[3]
Did it exist or not? The source says it did, so if no objections are raised, I'll remove this.
Only users with the gadget enabled would be able to see the highlighted text and comment in the article itself. The rest would only see it in the talk page.
Because of the way I'm thinking the gadget would work, if the wikitext/HTML of the parent paragraph changes (for example because the issue got fixed), then the comment would stop showing in the article to users with the gadget enabled. This is because the wikitext/HTML of the paragraph itself would act as the anchor or identifier that would allow the gadget to know where to insert the comment. This may be sub-optimal in some cases, but it's the only way I can think of doing it without having the gadget insert things into the wikitext of the article (which would be a definitive no-no). In any case, the comments would always be available in the talk page.
To be honest though, some of your comments have made me question if this could be useful, but I think given the way it would work, and considering it would be an optional gadget that won't be available to random visitors, it should be harmless, and time will tell if it ever becomes popular. I'm working on a crude prototype and will share it shortly. Any insights, ideas or comments are welcome!
Kind regards,