As of right now sims follow a standard 24 hour cycle. When a person arrives to a sim they can see it as the sim owner wished by going to region default, but other than that there is not much variation from sim to sim.
Since I have been in second life there have been a handful of "new" things to pop up which change the way we see or interact in this world. There are the unfortunate crazes like bling, but the big ones i am talking about are thing like sculpties. Or when voice was added.. or glow. some things make a huge difference and one which would have the same kind of impact across the grid is to allow for custom sky settings for sim owners. What this means is that I could use the already existing custom tools to build skies and have them set to region default. People would arrive to Immersiva and suddenly be put into not a mere sunset or nice sunrise but something new and different.
The sky settings would allow for every sim to have its own particular feel and would revolutionize the way we see second life in a relatively cheap alteration to the already existing code. What Linden Labs does right now is to have what they call jira's. Jiras essentially are wish lists that people vote on for a wide range of features. Linden labs looks to see which ones are the most popular and decide to work on them. I am told that if a jira reaches 500 votes then they will begin to take it seriously. So the jira for custom sky settings stands at 327 people voting for it. Its been sitting there for a year or so. Would everyone who visits this blog take two seconds to vote for this jira so that I may one day be able to have skies such as in the video below for all to see when they arrive at my sim. Here is the jira. Please vote.