I think it would be cool if parks actually closed for the winter months (or it could be turned on/off optionally.) like say, at the beginning of November, rides and shops are shut down and guests leave the park. Then towards the end of February, new guests slowly begin to arrive. This would cause a shift in profits, and players would have to plan accordingly. During the months of November-February, the park would have less expenses (no electrical bills) but would still have to pay employees who would be doing the usual maintenance.
We could even come up with different systems for the scenario editor, like maybe one scenario actually has snow causing guests to be unhappy and rides to be unsafe, or another scenario could stay open all year. Maybe handymen could shovel snow? (lol maybe thats too much)
Or maybe we could come up with an all new calendar system. Instead of having 8 months to a year, we could have a weekly schedule. Currently 1 month is about 7 minutes, so maybe we could switch 1 month to 1 day, and we could make a day last longer (1 day/month in Planet Coaster is about 12 minutes). Maybe with a day to day system we could have guests leave the park each night (though that might be too frequently).