Support varnish cache.
www.varnish-cache.org

Include memcache and settings for ram etc as standard.

add HTTP/3

I'll like to create a hosting that only use Nginx as webserver. Also I'll like to do this with Node.js, but I think it will not be approved.

Free version of Enterprise Litespeed, it would be nice to use lsphp+Openlitespeed+LSCache (free) within Plesk.

Add Redis support for Plesk for Linux so we can manage it directly via Plesk GUI

For now it is possible to manage specific TLS version and cipher suite only on server level, meaning that particular TLS versopm will be applicable for all domains at once. It would be nice if Plesk introduces the ability to manage TLS version per domain basis, which would add more flexibility for Plesk administrators.

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/

Currently it is not possible to make domain-forwarding for every Domain in an Abonnement. You have to select website-Hosting for the first domain to enable Forwarding for other Domains.

At the moment it is not possible to change or choose the vhost path for a domain. Every Domain is installed in the standard vhost path, at example /var/www/vhosts
If someone has a Server with attached fast and slow storage or big and small storage, it should be possible for the administrator to choose between them when installing a new Domain. It could be possible to give a customer service packages with faster storage for mission critical domains or giving him a lot of space for another domain located on disk drives mounted to another location.

An Nginx restart interval should be helpful for situations when users use API calls to modify domain's PHP settings. This results in multiple nginx reloads:

/var/log/plesk/rc_actions:

INFO: [Tue Feb 26 15:26:00 CET 2019]: Service: nginx, Action: try-reload
INFO: [Tue Feb 26 15:26:44 CET 2019]: Service: nginx, Action: try-reload
INFO: [Tue Feb 26 15:26:59 CET 2019]: Service: nginx, Action: try-reload
INFO: [Tue Feb 26 15:28:06 CET 2019]: Service: nginx, Action: try-reload
INFO: [Tue Feb 26 15:29:11 CET 2019]: Service: nginx, Action: try-reload

A similar functionality exists for apache in Tools & Settings > Apache web server > Restart interval.

Redirect http://hostname:8443 to https://hostname:8443 on Windows.

Currently only Plesk on Linux can do this.

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.

Please pay attation for the next releases:
https://plugins.roundcube.net/packages/johndoh/sieverules

Maybe you can use:
roundcube/managesieve (default plugin)

modbw cannot be used for limiting connection when nginx enabled. Plesk does not provide out of box enabling and configuring limitation of connections for nginx. Please add support for limitreqzone which provide similar functionality as modbw for nginx so that it would possible to control such resources.

Plesk seems to add up the request response size,
including those of its own extenal IP address.
We would like to disable this behaviour or filter out this info, because
this is not the actual traffic.

We have customers that have a lot of internal requests because of some
caching module where about 50% of the total traffic is from its own IP.

or provide a way to use nginx-full.

When tuning system for modpagespeed, http/2, PHP7 w/opcache, https, ran into issue with Apache, where turning modpagespeed off, then back on, or off then restarting doesn't clear cache. On a development site, I had to do a htaccess to fully disable in order to apply CSS changes which were 'stuck' -- a 'clear cache' option from panel would be super cool, vs command line ! :-)