I think this sounds a bit cheap to be honest, I'd have preferred an in-game menu to choose the campaign you want to play, no matter how it's programmed, just load the sdata you would load at gamestart when the campaign is actually started. I always wondered why some games load a lot of data to show the main menu anyway.

I was actually hoping for a much more integrated concept but guess that was futile, this approach should also make it harder to get addon units into the grand campaign since it sounds like you'll have to copy all the new data dn since the data is compressed into larger files you can't just copy the files etc.