There is an @nextcloud/designers group on GitHub. This enables people to just mention @nextcloud/designers in issues and pull requests to notify all designers. Otherwise you have to mention each one individually.
The main people working on Nextcloud design are:
Please let us know if you want to contribute to the design and would like to be in this group. You will be notified every time someone mentions this team in an issue, which would be every design issue or pull request.
You should also join the #nextcloud-design channel on IRC. We use this to communicate on smaller issues, talk about what to work on next, and just general chatter. It’s good to get to know the other people and for organization in general.