Whatever gets built in the next major investment, I would definitely not want it to be a coaster. They haven't invested in a proper family attraction since Battle Galleons*, and I think one is due. Unfortunately, we can't trust Merlin with a dark ride, so they may have to think a little outside the box.
An attraction that I really enjoyed at another park was Speed of Magic. I have no idea what its ride type is but here's basically what it does: Guests (wearing 3D goggles) sit in a single carriage that can hold about eight people. I moves through various rooms with screens. The screen plays a 3D film whilst the carriage moves around in time with it, once that two or three minute film is over, the carriage then moves into the next room where another film is played etc. Each room as a small amount of physical theming, some thing with Merlin know how to do well...
Here's a video of the ride:
This video also includes the ride's preshow.
https://www.youtube.com/watch?v=nwckAD4ik3U
It is totally soundless from the outside, perfect for coaster corner. Even a theme like Speed of Magic's would work in Cloud Cuckoo Land. The ride's throughput is nice and high, so queues won't get too long.
*By family attraction I mean something that everyone can enjoy, together, with no bravery required. So Thirteen doesn't count, neither does Ice Age or CBeebies.