I've been playing CC since 2013, been on the forums since 2014 and if there is one single thing that I've seen the most often, and the most consistently, it's the "I've lost my save" messages. The answer is always the same, and always simple: backup your save regularly, it will get crushed by clearing browser history and stuff like that. Yet since this is a problem only new players encounter, they would obviously not follow the forums, or reddit, or wiki or anything like it. I think a feature that could benefit to everyone would be some kind of in-game reminder for new players to constantly backup their saves.
I'm thinking a note at the bottom of the page (like all the normal poppups we get in-game), that appears each time you load the page until you have used either the "export save" or "save to file" buttons from the options menu. This message could be something like "warning remember to constantly backup your save" or whatever. The important thing is to teach new players that the automatic save system is not failsafe and backups should be frequent (preferably to clouds like google drive or pastebin in case your computer catches on fire or whatever, but i don't think this is necessary to say). Maybe you could also have this message start popping up again if you haven't used either backups buttons in like a weak or whatever. This could be disabled through an option for instance. Maybe the message itself could be short, but when you go to the options menu you would have a few lines at the top that tell you about saving, that your save can be lost, why you should save and how. I don't know, throwing ideas at the wall.
So yeah. Simple idea, simple change, big implications.