Since we are legitimizing these youtube covers, I still don't understand why we don't allow promotional copies of cover songs.
First of all, there is a major difference between "classic entries" and "web cover entries". The first category is well-documented, very detailed, regulated and moderated. The second category is much more loose on all these characteristics.
Second, promos are not allowed as classic covers because of their non-commercial and non-public behaviour. Of course, there is an exception to this rule for originals, but that would make hundreds of demos the "originals". This would be counterintuitive for the vast majority.
Lastly, wherever this discussion leads, right now nothing stops you from adding a demo as web cover.
All of this being said, I understand where the intuitive problem is. Would it be stupid to set the release date of demos as "unreleased", as to avoid them to be originals? It would be a way to integrate physical demos as "classic entries".
Demos are not promos. Demos are "recordings", promos are "releases".
In particular, a demo available on YouTube may (or may not) be "previously unreleased", a YT video of a song only available on a promo release cannot be unreleased.
The way I see it, a Promotional Video of a song, made available through YouTube, might very well qualify as an original (first release), as anyone can listen to it and, in theory, make a cover of the song before the song itself is released on CD, LP, MP3 or whatnot.
Same goes for songs that receive airplay before they are released on a physical medium. As long as it is legally available, it is officially and commercially available. Even though we may find no reasoning behind a certain "commercial strategy."