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

Please add Mailman support to Let's Encrypt.

Ideally, one could issue either a certificate directly for lists.domain.com or a wildcard certificate for *.domain.com.

Furthermore, a secure connection should be enforceable.

Thanks!

Let´s Encrypt already support wildcards, could you implement it to PLESK asap?

For example, Odin uses a system where all the website information is stored inside a NoSQL database, and apache just reads this data with a special module:

http://www.odin.com/products/automation/services-and-applications/shared-hosting-next-generation/

I think you should add HTTP authentication to the Plesk panel itself - that way it is more secure and if there is ever a vulnerability that allows bypassing the Plesk panel login, someone would also have to find a vulnerability in HTTP authentication itself before even getting to the Plesk panel in the first place. To me it makes more sense to make the Plesk panel itself the most secure it can possibly be, not just websites/virtual hosts hosted by the Plesk panel.

Ask for hostname during the initial configuration instead of setting the default one.

A process to support symfony projects

This is all about security, it's simply not a fully developed product without this facility and I am hugely shocked and surprised it doesn't already exist.

Allow the ability to assign separate SSL certificates for multiple mail servers.

Currently only the Administrators can manage site-aliases with the API.
Why is it not possible for customers to manage site-aliases of their own sites, while they can manage their sites and subscriptions ?
Now I have to use administrator access in the API on a single website, which is a security issue. This website can now manage everything. I would prefer to use the credentials of the customer to manage it.

By default, WordPress Toolkit creates instances with the same interface language as Plesk customer interface. Please consider adding the option to set custom default language for new instances.

The feature "Deleting a customer account now results in all backups belonging to that account being deleted as well" was implemented since Plesk Onyx 17.0.15

Add an opportunity to choose will the customer's backups be removed together with the customer or not

Update nginx to enable HTTP/2 Push, this would be great for many Applications.

Please add the functionality to add existing FTP account to different subscriptions.

It would be nice to provide mail SSL/TLS support with SNI for more domains from single IP

To be able to set specific security policy per subscription instead of server-wide.

Plesk Onyx is setting a random password for the psa admin database and the connection to port 8306 using the default admin password is not possible.There is no way of retrieving or reseting the psa database admin password which is causing big trouble if we want to connect to the psa database or want to change the default database using plesk repair

Often large Companies with lot's of Workstation are getting blocked because 1 Client in their Office is trying to log in with wrong Password (imap/pop/smtp) - then the whole Office of them is getting blocked and the search which PC/which User is causing the block.starts ...
It would help big times if one got a reference which Login Name / Username caused the block as additional Info next to the IP ...
Won't help on Brute Force Attacks where the Username changes ... but on this Scenario it would be a big Timesaver ...
Andreas Schnederle-Wagner

Enable IPv6 Only DNS through Plesk for windows server 2012 to publish applications in Apple store.

It is needed to list files for removal before it is actually done.