Thanks for the quick answer!
Understandable. Although regrettable for me. 
Sure! What I am looking for is the seamless experience between desktop and mobile. Ideally one would not need a Nextcloud account to open and work on a file together (at least on desktop). And if I have a nextcloud account there is the possibility to also work directly in the file on my mobile phone. (Both of which should be possible with OnlyOffice from NC18 onwards)
I do share quite a few files with people who don’t have Nextcloud. They would need to download the file, edit it offline and then re-upload it to the cloud. That’s plain and simple not good enough for most people who know Dropbox, box, GDrive, etc. (Not even talking about the fact that this is error prone if somebody else does this at the same time. And several versions of a document emerge. That’s THE collaboration nightmare). In the end I have to work on their platforms because mine is not convenient enough.
[Therefore my counterargument against your stance of OnlyOffice needing to support LibreOffice documents would be, that when we at least get OnlyOffice out of the box editing, at least your users can utilize Nextcloud and don’t have to switch to Dropbox or whatever non liobre plattform… Just a thought.]
The format used is not that important in my cases. That is why I am ok with only Microsoft formats.
The real use case of course is in a more formal/business setting, where people collaboratively work on presentations, studies, etc. I am okay with my private cloud not having this ability, but at my work-Nextcloud should have this ability. When I think that you want to serve collaboratives and collectives, where people work on a shared mission - i can imagine that such an easy to use solution would come in handy.
I don’t seem to have it activated. On desktop - When I click on files, they just get downloaded, instead of being opened in collabora online. How does it work? [It happened to me twice, that a file could be opened in collabora online on my Android phone. I was really happy, but it seems this was more of an accident, since I can’t do it reproducible.]
What!? You have already deployed « Nextcloud Text »? I have asked for it here: https://forum.indiehosters.net/t/new-app-request-nextcloud-text/3316 But since we are still on NC 16, where it is optional. I hoped it might be there when you update to NC 17.
Just tried to find it. An indeed it is there and I did not know! 
I just never tried with « .md » files in the « files app »… That is a nice surprise. thanks! In theory Nextcloud Text could suffice, although it seems like it has similar problems like codimd [see below] when it comes to mobile editing.
Yes, that is nice if you just work desktop only. But it does not work on mobile (Android). It needs some special app to open. Nobody has such an app. Therefore something written on the laptop can’t be opened later on the phone, which makes it useless if you have notes/text/whatever you can’t open when you don’t have a laptop with you.
A workaround for mobile editing could be to only save all my documents to the « Notes » folder and work on them with the Nextcloud Notes app (https://github.com/stefan-niedermann/nextcloud-notes)… But of course it would be good to be able to open files from all places in my Nextcloud…
Do you know of apps with wich you can open and in real-time collaborate on .md or .pad files (i.e. at the same time also working on the file via the Nextcloud on a laptop)?
