The official spot for Windows Feedback, including developer items, is the Feedback Hub app. Yes, it does get looked at. Items posted elsewhere (including these forums) often get migrated into the Feedback Hub for you, but you'll lose tracking by not doing so yourself.
For your specific Office 365 Calendar suggestion, you'll probably be best off on the O365 Developer UserVoice. That request is something that would be implemented by Outlook not by Windows. You should be able to access the Calendar with the current code via the Outlook Calendar REST API -- that's really a question for the Outlook specialists over in the Outlook developer communities.