It would be fantastic to have a year view in the calendar tab. We have often longterm dates like campaigns which are in the next few years. To keep the overview the year view, formerly existing via add-on, is very helpful for us.
This would be great if Thunderbird would be able to display a yearly with each row as a month and aligned by the day of weeks. So that every day can be seen and appointments/entries that are longer than one day could be shown as one single line over the days.
A very good and useful example is the software Essential PIM which I used to use back in the days when I was using Windows, because this kind of view really really helps in planning long term and easily keeping an overview of the year.
Please please add this to the new Thunderbird version 🙂
And I would disagree, that this idea is similar to the one that Jon has linked in his comment 🙂