I was trying to import the documents app in oc 10 and got the same results as you.
And as for collabora - I asked around and it's an enterprise feature.
The thing is - ownCloud is a file sync solution, all the apps are extra. Apps come and go as people are interested in them and / or have time to develop them. As for now there aren't enough people with free time, knowledge and will to develop the documents app, and a few others. If you are interested in the app - you can help.
So sadly documents app is gone, for now. You could go back to owncloud 9 though. Would that be an option for you?