good day Bastien

anybody can
'vote-for' a bug, and you keep a counter on voted-for.

It would require people to register on updates.orgmode.org.
I'm not sure the expected benefit is really worth it for now.

why would it?  you already trust email senders on identity and integrity in all ways, you can also add this one.  a user is an email address.  the benefit, in my eyes, is for you to have a measure of the opinion of (voiceful) users.

a maintainer can 'confirm' (that fixing that bug is
desirable). 

I think it is important that anyone can confirm a bug.

I see differences among -confirming a behaviour, -confirming that a behaviour is a bug, -asserting that a maintainer would accept a "correction".  please drop the subject if you don't want me to argue in favour of something you have already discarded.

That said, I would love to organize a hackathon for Org-mode where
people would gather online for one day, exchange ideas, break and fix
things, propose new features, etc.  That is, IMHO, the way to recruit
new contributors, on top of simply formally asking "who would like to
be in charge of X, Y and Z?"

I like the `#emacs' irc chatroom on freenode, I discovered it recently.  the more specific chatroom `#org-mode' is less active but not less welcoming.  it was there where I got the hint to write here, and where they told me "no need to subscribe".  or open a new temporary room, but I hope we stay with IRC, which we can use from within an emacs buffer.

ciao, Mario