I would really like to see this feature. And I think the reason for it is more apparent now that tags are a distinguished by a special color/toggle in graph view (like earlier posts alluded to)
Alot of people (especially a lot of ex-Roam users) work by using Tag pages ( aka #[[tag]] ) as a catch all or hub. More interestingly, a lot of MOC users do something very similar (and may not realize it) when they use MOCs. (I’m an ex-Roam users who loves MOCs now 
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The clearest way I can describe the rationale/functionality is this:
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The role of the tag classification is to distinguish from “regular” notes. The same distinctive role is often filled with the use of MOCs. Whereas notes are generally declarative statements or at least a few words, tags and MOCs are usually single words and more like umbrellas. I think everyone is in agreement here
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Being able to write notes in a tag page would allow you to use the tag as a workspace for incubation. This is why many MOC users use MOCs for the structure of their notes instead of tags – MOCs are tags on steroids.
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Using [[tag/MOCName]] obviously removes the phsyical distinction between tags and regular pages/notes, and even worse is not taking advantage of (imo) Obsidians biggest strength: visual representation–which, like i mentioned is even more useful in the latest update. MOC users currently have to sacrifice this functionality
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This probably leads you to ask why not just use “[[#tagpage]]” or [[moc_Page]]? Well bc when you use that as the heading of your note, then in order for the backlinks to pick it up, you have to always use #tagpage in your other notes and is completely useless when looking for unlinked mentions. This completely ruins the idea of the “smart hub.” Again, MOC users also have to sacrifice this function.
I think even more useful feature in the future (could be a plugin), would be other tag prefixes, such as @[[name/source/alternativeheirarchy]], for even more visual and theoretical distinction. Since Obsidian seems to be distinguishing itself from a lot of other backlink focused apps (especially roam) with its extremely powerful graphical views, this would play even more into Obsidians strengths, especially with a toggle and special color in graph view for those alternative prefixes.
(edited for clarity)