Peter Pan's Flight really does have the potential to be a truly great dark ride on par with POTC and HM if they were willing to rebuild it somewhere else. I'd say behind IASW, Mermaid and BoG is the best fit. Take up IASW's old space after relocating to the new area.
Taking up all that space, you could probably work in -
- Near the area behind Big Thunder and TSI, Bald Mountain (MK's first true-blue thrill ride with a 48"-54" height requirement), Nightmare Before Christmas show (if they refuse to retheme Haunted Mansion to NBC during the holidays) and a Sleepy Hollow dark ride
- C-ticket Tangled dark ride by the bathrooms (3 minutes - nothing too fancy, but still nice)
- Neverland mini-land with Peter Pan's Flight in grand fashion (lavish facade, actual AAs, detailed sets and a 10 minute length alongside a high capacity ride system/RV), a Tinkerbell/Pixie Hollow M&G, and a Jolly Roger play area (replacing the Casey Jr. splash area as the water play area for Fantasyland)
- Wonderland mini-land with Alice maze, Cheshire Cafe, Tea Cups and newly themed Caterpillar coaster (Barnstormer gets relocated)
- Diagon Alley-esque theming for an Arendale section including a new Princess Fairytale Hall, a trackless dark ride themed to Frozen and an Olaf flat ride similar to Mater's Junkyard Jamboree
- Pinocchio shoot-the-chutes mixed with a standard family dark ride (basically a mini-Splash Mountain, but still on an E-ticket scale) by Storybook Circus
Likewise, it would open up the opportunity for the following
- Casey Jr. Circus Train is brought over to MK, but in a new form that includes some theming/show scenes along the way (replaces Barnstormer and a little extra space)
- The old Tea Party/Cheshire Cafe area is rethemed to Pooh. Tea Party's space is used for a Hunny Flyers flat ride (mini-swings themed to a beehive inside a tree) and Cheshire Cafe's old spot becomes Rabbit's Hole
- The old Peter Pan building and bathrooms could be used for a Mary Poppins dark ride with a larger queue
- The old Princess Fairytale Hall could become a Sleeping Beauty/Maleficent dark ride
- Mickey's Philharmagic could be relocated to Town Square Theater. Thus, the old building could be used for a new show or dark ride themed to an underutilized IP
This would give Fantasyland
- 8 dark rides (including 2 E-tickets and a D-ticket)
- 3 coasters (I kiddie, 1 mid-level and 1 thrill)
- 1 water ride (relatively all-ages... maybe a 32"-36" height requirement)
- 1 track ride (Casey Jr.)
- 3 shows
- 5 flat rides (all slightly different)
- 1 play area
- potentially 5-7 M&Gs
While some might think 22 attractions in Fantasyland may be a little much, think about how much of the day most toddlers/preschoolers spend in Fantasyland to begin with. Aside from POTC, HM, Jungle Cruise and Buzz, I can't imagine they do much else outside of Fantasyland unless whoever took them had a certain show/ride they wanted to do in another area. It would ease the capacity issues for Fantasyland, give adults and teens some more to do (Bald Mountain, trackless Frozen dark ride, revamped and extensive PPF, SDMT, Sleepy Hollow, Nightmare Before Christmas) when in this area of the part, and reinforce the idea that WDW should be for everyone... not just little kids. It's not sacrilegious to add one thrill ride to Fantasyland - adults like fantasy, too (HP, LOTR, Narnia, WoW, Game of Thrones, Studio Ghibli, Greek mythology, etc) and Disney shouldn't exclude other forms of fantasy because they aren't all-ages.
Yes, all-ages dark rides should be added to other areas of the park (a people-eater in Tomorrowland and Frontierland would be appreciated... a small Fantasyland-style one themed to Jungle Book could fit in Adventureland, too), but most little kids want to go to Fantasyland for the vast majority of the day. So give them a day's worth of adventures/attractions!