Wow. From a simple suggestion we go to a total overhaul of legends mode. Its a great idea though. It doesn't even need to be a complete redo. Just look at how sites are usually displayed in legends, then add a greater level of detail for user-controlled forts. Knowing Toady, though, I think that adding grudges and personal gossip into one site will eventually necessitate putting that sort of detail in ALL sites. And while that would be awesome I would have no idea how to go about it. Maybe for the language and personality arc there will be some updates on that score.
And eventually the timelines that are loaded into fortress mode on the units screen could be dumped to legends after FUN happens! We could go see all the units from the fort, when they migrated, and maybe even their history from before they came! Now that the next release contained ACTUAL migrants instead of those random-generated ones, I can see this as becoming possible.
Which brings me up to one last point that I really wanted to make. Since migrants ARE procedurally generated as part of the world, maybe their pre-history can be uploaded to the timeline as well. If we're lucky, it could spit out a reason for why they left! (War, disease, wunderlust, etc.)