We mainly use this package in our custom plugins to give customers an update feature much like the WordPress update feature. It would be great if there would be a way to hook into this.

https://github.com/YahnisElsts/plugin-update-checker

My assumption is that plugins and themes that are not hosted in the WordPress repository can't be automatically updated. Premium plugins and theme that are hosted will (for as far as I know) be updated automatically.
It all depends on how the author built the plugin or theme.

That‘s right! I know that MainWP can update all plugins and themes remotely, premium or not. Probably you should take a look at this mechanism.
Here are some more general information: https://kinsta.com/blog/wordpress-automatic-updates/#wordpress-automatic-updates
https://code.tutsplus.com/tutorials/a-guide-to-the-wordpress-http-api-automatic-plugin-updates--wp-25181
https://wordpress.stackexchange.com/questions/194030/how-wordpress-detects-a-plugin-update

Here is a concrete idea:
https://github.com/YahnisElsts/plugin-update-checker

Hope this helps to implement this feature as soon as possible :)

Take a look at mainwp.com. They implemented this feature some time ago.
https://mainwp.com

I agree with nbadmin. Ability to update all plugins is mandatory. Should have been implemented from the very beginning!

Seriously? That's your intelligent response?
Guys,
Plesk is probably used primarily by people who use your software professionally.
And they usually work on several websites at the same time and need to keep customers' websites up to date so they need to maintenance them.
I use at least 60 premium plugins, and I also use self-developed plugins.
That Plesk can only update free plugins automatically i never have occurred to me when I licensed your software. Write to all Plesk customers and ask if they care about the feature, and you will get 98% of the feedback that they expect it.

Try to act smart and not with polls in a forum that only 5% of your customers read at all.

This is way more than a must-have feature! It's an essential core feature and as a paying customer of Smart Updates, I will cancel my subscription if it's not available soon as it makes absolutely no sense to update 30% of my WordPress installation automatically and 70% manually. It even takes more time when doing it in two different ways. So please implement this feature ASAP.

This function is a must. Sorry, but that the function to update paid plugins is not implemented from the beginning is very unprofessional for me. This is a must. Check it out at MainWP. They do it right.

The same goes for premium themes, of course.

As most Webdesigners use paid Plugins or there is no "non paid" version of alot of plugins and themes, updating all those things like it is done when login inside every site aand press update, just on the fly with the toolkit would be great. At the moment the toolkit and the paid smart update is kinda useless as it does only update a very small part of the themes and plugins so i have to login in every site myself, too to check for updates on premium plugins, themes and so on :-(