Keep two (or more) Plesk servers in sync for a failover scenario.
Migration Manager only allows manual "sync"

Net core can run applications on windows and linux with a short configurations . Please add support to both OS

Is easy to use.

Support varnish cache.
www.varnish-cache.org

Firewall should be able to block the IP of the selected country. I have a lot of traffic from the IP 5.10. *. *

ActiveSync is a necessary tool for most businesses today as it allows them to have everything in one place and stream it automatically to every device they use. Users with mobile phones and tablets can easily sync their contacts, calendars, notes and emails via activesync and users with outlook and other mail clients can sync contacts, mail and perhaps notes.

Include memcache and settings for ram etc as standard.

It should be possible for the admin user to change his user login name. The name "admin" is not very secure, because it's easiert to hack via brute force. The hackers know, the name is "admin". If the user would be able to change his login name, it would increase the security of Plesk Panel.

Make separate limits on Mail and Web disk spaces, so that hoster could sell one limit for web (i.e. 2Gb) and another limit for mail (i.e. 10x2Gb mailboxes)

add HTTP/3

Add Sogo as a webmail alternative in Plesk.

Sogo share your calendars, address books and mails in your community with a completely free and open source solution

Sogo is a great webmail solution and provides native Microsoft ActiveSync support. Mobile devices such as Apple iPhone, Android, Windows Phone, and BlackBerry 10 can fully synchronize emails, contacts, events and tasks with SOGo.

Add a new Domain/Subdomain-Type "DynDNS", which redirects to a dynamic IP-Address like dyndns.org and similar sites including an api to sync the current ip address through url call.

PIWIK is death!
Simple Matomo-plug-in installation without additional configuration for the databases or the host

Now you have two opportunities to set the spamfilter - server-wide or individual. It would be very handy if the admin or the customer could set the spamfilter for the whole subscription or/and for the whole domain.

You are currently not able to Alias a subdomain through plesk. Instead you must create the subdomain as a primary if you wish to alias it. In many situations it would make sense from an organizational standpoint to keep the subdomain under a main domain while still adding aliases to it. I do not believe this is a technical restriction of the webservers so it would be helpful if plesk allowed you to add aliases to subdomains.

It would be nice to have an external SMTP (smarthost) ability for a per-domain basis (most mail services have this)

We use this for external scanning, data leak prevention and more.

Can this be be done?

If I use FTP, I can make as many users as I want. For various reasons, using FTP is not optimal at my workplace. I'd like to be able to let each ftp user I create log in with chrooted sftp.

I'm able to modify /etc/passwd and /var/www/vhosts/example.org/etc/passwd to make it work, but doing that manually kind of defeats the point of using a tool like Plesk...

Specifically, I give the ftp user the same home directory, and shell as the initial sftp user has in each passwd file.

t would be a good idea to have an SQL section where users can run optimization scripts like MYSQLTUNER etc and enter suggestioned changes in a GUI that directly change the mysql.conf directly and correctly.

An ability to monitor performance and tweak would be ideal, making the task of SQL performance monitoring and tweaking far easier.

Also optimize commands and other tasks could be run for this panel.

as well as optimize and the ability to add it to cron for weekly or monthly.

What about DDOS Protection in Plesk?

As we have to use apache, i don't like to go for an aditional nginx proxy just to simulate HTTP/2 ;-)

I think apache is capable to handel HTTP/2 :-D