Going back to one of the original issues with subdomains that has been a problem since 10 came out, there is no way to create an FTP user that can access the subdomain's httpdocs directory and directories outside of httpdocs (such as cgi-bin).
At least in 10.2-10.3 you could house the subdomains/cgi-bin under the mail site's vhosts/DOMAIN/subdomains/xyz and the main FTP user of DOMAIN could get to those files, but now with the new vhosts/SUBDOMAIN struction, the main FTP user has no access since they can't go above their home directory. The vhosts/SUBDOMAIN directory is owned by the same main user as DOMAIN, but there is no way to access those files via File Manager or FTP.
Creating an additional FTP user only allows them access to the httpdocs for that subdomain.
Also, the subdomains settings contantly changing with every version of Plesk now is a support nightmare, since customers and support staff have to be kept up on where their subdomain files just suddenly disappeared to. Now with the extra subdomains no longer being accessible via FTP, scripts and software that relied on this access are broken after upgrading to 10.4.
If I've missing some magic way to access vhosts/SUBDOMAIN via FTP or to create an additional FTP user that can access ALL of the directories related to a subdomain, please provide the steps, Parallels!