I love Pendragon's Arthurian setting, but being a tinkerer, I've been thinking about what other settings this great set of rules could be applied to, such as CAS's Averoigne, or C. L. Moore's Jirel of Joiry, or a romanticized campaign set during the crusades, al la Kingdom of Heaven.

What such efforts have being tried by you?

I have GMed a one-shot of Middle-Earth set in the ending of the Second Age (The Last Alliance of Men and Elves). I have been meaning to do a campaign in Middle-Earth, encompassing the Third Age, but the amount of work involved has been a hurdle, as is the fact that I wouldn't, currently, have any time for new campaigns anyway.

I could see Pendragon adapting easily to Game of Thrones, or, as you say, historical campaign. Another 'maybe some day' idea would be to do the Wars of the Roses, or the Hundred Years War.

I started a similar thread fishing for potential settings on rpg.net recently

I'm back working on the first age middle-earth setting now

http://forum.rpg.net/showthread.php?612557-Alternate-settings-with-grand-campaigns-for-the-Pendragon-system

I've started preliminary work on a campaign set in Averoigne, the medieval setting for several short stories written by Clark Ashton Smith. CAS was a contemporary and correspondent of HP Lovecraft and Robert E Howard and contributed to the Cthulhu mythos. This would be a Medieval Romance/Cthulhu Horror campaign :o, and I can't think of a better rule system for it than Pendragon 4th Edition. Give the stories a look if you can, they're worth it. :)

Sounds interesting. I'll check it out.