I think Anne of Green Gables needs to visit England. And dance at a ball or two. Gilbert Blythe with a British accent? Yes, please!
Heyer's Regency England setting would be a very interesting combination with Allen's magical realism.
Can you just imagine what this book would be like? Wodehouse's brand of craziness would ensue with a minotaur or two thrown in for good measure.
I want more Harry Potter books, period. But if I could get them with the deeper level of symbolism and meaning that the Chronicles of Narnia contained, I would be in heaven!
Combine one of Jacobs' crazy antics with Bryson's narrative style. Or better yet, have them both participate and tell about their adventures in alternating chapters!