The Founding of Madripoor was one of the innumerable writing ideas I'd had, but was forever too lazy to actually follow up on beyond the fun part of screaming over the din of the Bishop and Belcher. "No. no - listen! and then we have Reagan stab Stryfe in the face with Namor's trident!"
The 16th century is one of my absolute favorite historical eras. The idea of putting together a story of the contemporaneous establishment of a Pirate Republic in the Far East... man that hit pretty much all my buttons. Wolverine would be there, of course, and the Hand, but also Bloodscream and the Honorable Company of Landau, Luckman, and Lake. Samurai exiles and pirate kings, ninjas and Venetian spy-assassins, British trader-adventurers, the Hellfire Club, and the Jesuit scholar-priests...
Intrigue, sea battles, the diplomatic maneuverings of the young Western Empires clawing out their place in the world at the expense of the aging principates of the yeasteryear.
A frontier kingdom in the Orient.
The closest I'd come to actually writing it out was when the X-Project unwisely required me to do a wiki mock-up for Madripoor as part of a plot I was proposing. The mods at the time was understandably pissed when instead of a three paragraph entry they ended up with a demographic, political, and social overview that ran to 15 pages, iirc.