There are a lot of amusing seasonal features that get added to the server every year: jetpacks, now RC vehicles, etc. I think it might be fun to allocate a certain amount of time in the server during which those seasonal items and other ridiculous things are available in any map-- Hydras, all the RC vehicles (including the Baron), jet packs, Sea Sparrows, maybe allow Vortex DB, etc. Not only would this add a significant amount of variety to maps that rarely change, it would also give ample opportunities to test out potential changes to the server, like messing with the SWAT weapons set, adding moving objects (like a moving ship?), or whatever other changes that would otherwise be possibly disruptive to just stick in the game without testing with a fair number of people.
I'm not so much suggesting what changes would actually happen during these periods as I am suggesting that the periods be created with at least simple changes to start with (like adding just Hydras and jetpacks, for example), then further additions to the mode would be suggested.
I don't know what the mode would be called, but it would be nice to show some change in the server name/gamemode in the SA:MP server browser so people know when it's happening and can join. Periodic announcements that the server is going into the mode or is in the mode, or is going to go back to normal in t minutes would also be good.
I don't know how often or for how long these times would be, maybe once every 23 hours for an hour (so the time moves around and doesn't only benefit certain timezones), or maybe a whole day around once a week or something.
I think figuring out whether people actually want to have this mode added is the first step, then if so, figuring out for how long the mode will run and how often, then deciding what will be in the mode are the following steps. I'm just trying to give an idea of what might be part of the mode, so please don't pick apart the hypothetical features I've suggested and save your feedback for just the idea of having the experimental/unusual features mode periodically in game.