Some speculation, as Chessington haven't had a brand new ride in a while. The park is in reasonable need of something new that can add capacity, given that pretty much every weekend Vampire and Dragon's Fury will have queues 40-90 minutes in length, along with Grufallo and Zoofari having similarly long queues.
If I remember correctly, there was some suggestion in the last development plan that they wanted to add a new coaster, with a water coaster being hinted at. Given the re-theme of Tiger Rock this year, I'm not sure they need a water coaster, or that it would give the capacity they need.
My speculation is given the success of Wicker Man, could they build a family oriented woodie? They could even shove an IP in there like Oscar's Wacky Taxi if they really had to.
The field at the corner of the Vampire and Dragon's Fury has been earmarked for development for a fair while, and I could see it nicely housing a wooden coaster, given how they've implemented Wicker Man.