P.S.: I don't think they should change the World Showcase Adventure. The KP theming is just fine as it is. And I actually think the World Showcase Adventure would be harder to change than, say, Sorcerers of the Magic Kingdom or the Midship Detective Agency anyway (especially when you consider the fact that unlike SotMK or MDA, which heavily rely on screens, KPWSA uses actual animated physical props).
Besides, KP's theming is a far better fit for Epcot than Phineas & Ferb. Also, as I've said before, Doofenschmirtz does not try to take over the world like the KP villains do, just the tri-state area, so in a way, it would be out of character for Doof to go that far. Also, the Phineas & Ferb characters don't really travel the world in the way that the KP characters do anyway.
Keep in mind that one of the reasons Walt created the theme parks was so that the company's characters could have a place where they would be guaranteed to live forever for sure, even when they weren't getting as much attention in other media. And that means let Kim, Ron and company stay where they are in the parks...and that means the World Showcase Adventure should retain the KP theme.