It would be helpful to have an ex-dividend date and pay date added to the calendar for tickers that have not yet officially declared their next dividend. I envision these entries appearing in a different color to indicate that they are only projections until the official dates are available. On the Dividends tab, you already provide estimated which is helpful for forecasting.

It should be possible to estimate the next ex-dividend and pay dates by looking at the dates recorded in previous declarations and calculating some kind of average (using the last 3 or 4 declarations would make a reasonable estimate in my opinion). For my own estimates, I usually add about 4 weeks (28 calendar days) to the last ex-date and pay date when a dividend is paid monthly, for example. It doesn't have to be perfect, and of course this calendar entry would be replaced with "real dates" as soon as the dividends are declared.