One good thing to note about Zulip over Rocket.Chat is that Rocket has a 10,000 push notification limit... If you have 10 users sending 50 messages over one month, you're already over the limit! 
There are some github support packages you can pay for ($5/$10) to increase your push notifications to 15k or 20k, but after that you have to pay. In this day and age. Push notifications are a must! 
I understand they get millions so need to pay, but not being able to buy more than 20k makes this a bit problem as switching to Rocket cloud is very expensive 
I'd love to see Zulip on here and even though it's not as easy to use, I've tried Mattermost, Rocket and Matrix/ Element and so far the other issues include; Mattermost CE has no user role/ permission management and Matrix is encrypted (albeit optionally) which I don't want for internal comms as we need to be able to audit it (like you would company emails).
Zulip is ideal, but I would love to see it on Cloudron so it can be managed with other Cloudron apps.
At the moment I have two Zulip setups and two devices with accounts on each, neither of which are getting push notifications (yes I've set it up properly). So once that is solved having Zulip on Cloudron would make life much easier.