I would like to see support for the upcoming MySQL 8.
Currently there is no support inside plesk and using a possible workaround with docker isn't possible out of the box.

MySQL Community Server 8.0.4 is already a Release Candidate.

Implement http://www.wildfly.org/ instead of deprecated Tomcat

Created according to the comment from this article https://support.plesk.com/hc/en-us/articles/360000322173?page=1#comment_360000633734

It would be great to have ftp account with an expire date.
A sort of temporary ftp accounts.

This becomes really usefull when you need to share your ftp details temporary with a webdeveloper, or somebody else to maintain of check an website.

I always make a new FTP account for this sort of events, but then forget to delete them. It would be real nice if you could set a expire date that the account automaticly blocks itself after that date is past.

According to a ticket I just opened (80693) Plesk currently doesn't support a clustered MySQL server, e.g. an active/active Galera cluster.
To avoid data-loss or corruption in a server crash, I'd like to run MySQL in a Galera cluster to automatically sync the data again once Plesk's MySQL started after a crash.

Have the ability to provide more Nginx builds/packages. For example, offer a 'nginx-full'-package with more modules.

For example, I need the Nginx headers more module. Since this need to be built-in at compile time, it isn't possible to add this later on. So that would mean replace the Plesk version of Nginx with the distro-default. (Heck, why does Plesk need it's own Nginx-build, anyway?)

No, passing headers from Apache is not an option, especially when I'm using the Nginx - PHP-FPM setup.

This would allow you to see mailboxes that are no longer in use.

Add mcrypt module to Plesk PHP 7.2 and newer.
For previous PHP versions it's included out of the box.

Mcrypt 1.0.2 natively supports PHP 7.2+ (https://pecl.php.net/package/mcrypt/1.0.2)

It's, for example, required by Prestashop 1.7.x, which is quite popular among Plesk users.

Currently the main domain must be renamed to change the main domain. This is cumbersome, especially if e-mail addresses are still assigned to this domain, because they will be also renamed. It would be more convenient if another already existing domain could be set as the main domain, e. g. by clicking on a button "Set as main domain".

Review an email's delivery route like Track delivery of Cpanel

Many times I find that some subscriptions won't sync because they are locked. I'd really like to know why they are locked. So far, I've been able to unlock & sync with no noticeable changes. But I'm left wondering what caused the lock in the first place. And I'm afraid that I'll realize later something no longer works as expected.

Having multiple DNS Templates, ideally selectable in a Service Plan, would add a great deal of flexibility in Plesk. For example, we have one type of Subscription that involves external store-and-forward mail servers for email backup. When a customer selects this type of Service Plan we have to manually adjust the DNS records to point to the appropriate mailservers. So it would be great if we could define multiple DNS Templates, then select the appropriate template in the appropriate Service Plan.

The implementation of the centralized smartermail in plesk onyx for windows is good, but it should also be possible to integrate this feature into the linux edition.

Many hosters provide both windows and linux hosting with ONE centralised mail solution. Since the integration for winodws is already done I suppose it shouldn't be too hard to integrate it into the linux version as well since smartermail is completely API based.

A carddav and caldav Server

Please compile nginx with these extra options to provide even faster time-to-first-byte responses on modern kernels:

./configure ... --with-cc-opt='-DTCP_FASTOPEN=23'

Background information and complete guide: https://www.masv.io/enabling-tcp-fast-open-nginx-centos-7/

It would be great if it would be possible to create multiple users which can use the Git repository. Today only one user can access the Git repository. It is the admin user which was created during the creation of the subdomain. New created Web Users for the subdomain can not access the Git repository. It is a feature which I am missing because I wanted to host a private Git repository for our small private team.

https://talk.plesk.com/threads/can-not-create-new-users-for-local-git-repository.342409/

I would love to use exchange server 2013 while using plesk panel. Exchange server is by far the most superior email server for windows and would be a great addition to plesk panel.

I believe that there is also an open API or an easy way to send commands which would make it a lot easier to integrate with.

Allow users and admin to select subject lines and keywords as well as keywords in the email body to be added to the spamfilter blacklist.

Currently spammers are just changing domains and sending the same email templates.

There is an spam filtering option to "Move to spam folder XXXX" on Linux, but not on Windows (Plesk 11+).

Unfortunately, horde doesn't work so well and every time when a message with broken header arrives, horde displays "Invalid Address" and no subject to all inbox messages. The described fix in https://kb.plesk.com/en/121175 doesn't work in this cases, forcing us to find the broken message manually (or scripting something to do the dirty job).

This feature should exists in Windows env as in Linux.