There’s a lot to say about the paid plans.
But
Here I’m gonna be talking about upgrading the free plan :
1-
Customization for the loading screen (so the user is not getting an “out of space” experience. Cuz having a happy fish loading screen with colors is not what you need for a pirate themed, World War themed, role-playing website)
It would be customized using an HTML file, and you can add .js files, .css files, etc… as usual.
The template for the loading screen would be the basic loading screen, no need to change the basic one if you ever add the customization feature.
2-
Server restart detection
Basically code that runs on server restarts when there is a code change. So when you make a change you can call all the clients and make it reload the clients.
The target of this feature would be pushing updates and ensuring clients are all to the right versions. Not everyone needs this but I currently need it and I’m currently looking for something that would allow us to make updates on clients look much more like what’s currently used by Discord.
3-
Server restart after downtime
Basically code that runs when the server restarts after it’s down due to a glitch issue. You can call the issue error code and get the date/time of the downtime, the status and all the infos we get through the email notifications.
4-
Glitch documentation about the custom JSON events handler I talked about earlier
5-
Getting data about app downtime, uptime, HTTP request counter, etc…
So we know for how long our app has been running/sleeping and we can manage efficiently our websites.
6-
Custom page reloading (when you view your project on an other page)
When glitch reloads the page you should be able to choose to reload the current page or go back to the main page.
My app is not on the main page (as this is the authentication page) so it reloads this one and I need to go back to the page I was working on again.
7-
New setting - Auto update (on/off)
When you update your codein the editor it also updates the server version. (not going into details so everyone can follow what I want to say)
When you turn this setting off it does not update the server version.
You should be able to update the server version when the editor version is ready.
And you should be able to run the editor version through the App Preview. When accessing the website through the URL tab it will show the server version as usual.
When you push an update (updating the server version to the editor version), it will trigger the server restart detection I talked about earlier.
8-
Glitch editor detection
If the code is running using the App Preview or not.
So you can enable developer tools automatically.
9-
Add a link for viewing permission when an app is private.
I don’t want everyone to see the code, but I still want some people to see the code (because I know them).
10-
Glitch translation app services
As multiple websites have translations, maybe having a place where we can put strings would be helpful for translation teams, website viewers, so it’s easier for everyone to get translations and we wouldn’t have to use external websites for this.
It would basically be a translation website but ony for Glitch projects.
You’d be able to set authorisations for users, call for help, etc… the usual Glitch community stuff 
You’d also be able to get money from translation if the owner sets prices for words/letters/sentences/string.