As to whether the USFSA will allow Kimmie to be beaten if she doesn't skate well:
1996 - Michelle Kwan US & World Champion
1997 - Tara Lipinski US & World Champion
If there is a 'Tara' (say Rachael Flatt) in the wings, USFS will let her beat our current 'Michelle', Kimmie, if Kimmie doesn't skate well.
(And Michelle in 1996 beat an awesome skate by Lu Chen. Kimmie just sort of fell into the World championship, what with Irina, Michelle, Yu Na and Mao not there and Sasha skating dreadfully.) Kimmie is no Michelle (96 version), so Kimmie will need to bring her A game.
There are some major, major differences between today and 1996-1997. For one thing, Tara was not subject to age restrictions since she had skated at 1996 Worlds at 13 and was grandfathered in under the new age rules. Tara was 14 in 1997, and she was eligible to go to Worlds.
Tara was also something of a prodigy, with a 3L3L combination that no one else was doing, had finished 3rd at 1996 Nationals, had skated in the GP, and was the 1996-1997 GPF Champion. Meanwhile, Michelle Kwan had to drop out of her GP events that fall with a stress fracture in her toe and as a result she was unable to do her 3T3T combination.
So you had a situation where these two ladies were equal or close to it on paper (Tara stronger in the technical area, Michelle stronfer in the artistic) and both had impressive competitive records.
Interestingly, the following year, TARA was the World Champion and again GPF Champion, and MICHELLE won her US crown back, and the 1998 World title as well.
Today, you have World Champion Kimmie (who is neither a Tara nor a Michelle), but there isn't a Tara in sight. Emily did win US bronze last year, but in the two years since she first appeared at the US Championships in 2005, Emily has just two medals: a bronze at 2005 Junior Worlds and a bronze at Cup of Russia 2006. Rachael Flatt is an excellent skater, but she's never skated at the Senior level at the US Championships before and her only international event was the 2005 NACS, where she placed 3rd as a Junior. She lost the US Championships Junior title last year to Megan Hyatt. And at 14, Rachael won't be eligible to go to Worlds for two more years.
There's just no real comparison there.