This sort of idea is part of many, many mmos out there, there is always seasonal events and special events and all that sort of junk. While I don't think haven needs a christmas or halloween event or anything like that, the idea of having special events or content that changes on a monthly basis could be very cool.
With seasons coming, say for the sake of argument that 1 entire stretch of all the seasons takes an irl month. Wouldn't it be cool if at the start of each month we got a popup, not unlike the meteor popups, that gave us a brief and fun forecast of what type of year it will be?
Perhaps with each iteration of a year, a bit of lore and fun story can be told, ushering in a few tidbits of new content, and perhaps even limiting already existing content. Maybe one year is particularly hot and dry so mushrooms will be very scarce, swamp curios will have reduced spawnrates, but there will be an abundance of things washing up on shores, animals will be more likely to spawn near water, perhaps a new couple bugs or birds or herbs, or even a new animal is seen during this year. Other years could be particularly damp and humid, cold, or simply whimsical and magical. Maybe some local resources have spawn timers reduced or elongated. Maybe entirely new local resources could come and go with these changes.
After this month is up, the new content specific to "hot and dry" year is gone. These couple herbs, birds, animal or w/e additional curios and junk that spawned for 1 month are simply no longer available until another year that has similar traits comes our way.
Having content like this could be a little more motivation for people to sign in throughout the year, even after burning out. See what content they missed or what is going on at the time. It would also give trading and markets a big boost since there will always be a short list of things that are not available for atleast a couple months, and would therefore be prime trading materials.