The addition of an encrypted calendar that would sync across devices would be most welcome.
I too would strongly prefer to make my ProtonMail accounts my exclusive solution for emails, contacts, and calendar management. As an email solution, it can't be beat! I still have to maintain a separate email account however to be able to manage my personal and business calendars. Please consider adding a calendar feature to ProtonMail!
Ted Goldstein commented
The lack of this feature is what keeps me undecided about my future commitment to ProtonMail. I have written them before to let them know that if encrypted calendaring were included they would have a life long loyal customer.
To consolidate votes, people who have voted on this thread should move their votes to this one instead (it has about 2300 votes at this time) ... https://protonmail.uservoice.com/forums/284483-feedback/suggestions/7187339-calendar-integration