Do I read correctly that this is related to "rsync daemon" (rsyncd), and therefore has minimal impact on people who just use rsync over ssh?
I guess the main takeaway is to be careful using rsync connections to machines that you don't trust.
Which (in my paranoid opinion) is pretty much the only secure use case anyway, for code like rsync.
Not quite. If server has "command=rsync ..." in ~/.ssh/authorized_keys file, for some ssh key (to allow rsync access, but deny shell access), this vulnerability will allow attacker in possession of that ssh key to go around that restriction, and get shell nonetheless.
If I was running an rsync daemon facing the public, it would be in a chroot with dropped privileges.