I got the chance to update to version 10. Currently running as a VM in Hyper-V on Ubuntu 16.04. A couple things to note...
Don't forget to save a copy of any theme folder you may have created and paste it pack into the /nextcloud/themes folder
You'll have to go back into your config file and enter the theme folder name back in as this got removed during the upgrade process
I proceeded with the upgrade via the web page. Once the new v10 folder was created and config file and theme folder copied back, I simply launched the upgrade from the web page. It's a very small install so only took a few minutes to complete.
I had installed the "disclaimer" experimental app on the previous v9.0.53 install and not really surprised that the new install got rid of that. If there was one request I would make it would be to include some version of the "disclaimer" app as a supported app in a future release. This is a very easy way to make sure the terms & conditions are available right from the application.
Will report back if there are any issues but so far so good! Nice job!