Once we release our first release of Nextcloud (for which we will provide easy migration paths as stated at How will I be able to upgrade to Nextcloud from ownCloud?) installing the apps will be a breeze.
We didn’t yet discuss whether we will just keep using the owncloud/calendar or owncloud/contacts repository. That should be completely fine as well since it’s AGPLv3 licensed and does not require any signed CLA or so.
Anyhow, the most important message is: We will strive to make it easy for people to contribute and we will ensure that calendar and contact are fully supported apps by us. We will let you all know once we have discussed some more how we should go forward on that 
That’s awesome! Thanks a lot for helping making the world a better place 
