We're not including a Calendar app. There's no particular reason that we need to bundle one and there isn't one available meeting our requirements.
You're welcome to work on adding a dark theme to the Contacts, Calculator and Messaging apps. It's an extremely low priority for us and you can also simply use different apps.
GOS Launcher needs to allow app name/label changing in both drawer and home screens because many apps have long names/labels that get cut off. Disabling app labels completely in drawer and home screen should also be introduced.
It's not included in the stock Pixel OS and we don't want to add it. You're free to use a different launcher.
Changes I suggest aren't important to security and/or privacy, but without them GOS doesn't look unified/cohesive. It should be fairly simple to at least have Contacts and Calculator apps support Dark Theme...
If someone submits a well written and well tested pull request, it can be merged. No one has done this. Dark theme was added by GrapheneOS to the Dialer app and we haven't gotten the help needed to maintain it. If we don't get the help needed then it may go away again. There's no one contributing that's working on these areas and it's far outside our focuses / priorities.