A Boomerang would be too tall and a Disk-o has no throughput at all (see Kobra or Airbender) not to mention the fact that they are a terrible ride experience as well. I still think a boat ride retheme (4th theme) for CATCF, a flume, return of the Toadstool, some use for the buildings (return of a soft play area, maybe some unmanned attractions like Nina's) with driving school down the far end. Theme wise? Not too sure tbh, Nicole's suggesting of an entire carnival theme might work
I get where you are coming from, A boomerang wouldnt be to tall, because theres so much you can do with it, I wouldnt want them to get the same one as drayton manors down the road, they could litrally get away with getting a tiny version. Anyways, out of all the areas in the park, CCL is the one where they can build pretty high in as all around it is blocked, Yeah theres a hiss behind it so you cant skim the tree line like oblivion but they could get away with 40-50 feet which is more than enough for a jr boomerang. This would also offer a ride similar to the RMT which is needed with towers, although I think SW8 will fill that gap.
The disc-o now you mentioned throughput is probably not the best idea for towers, however according to wikipedia the model with 40 seats can get a throughput of 1000 people per hour, which is enough for towers. I cant imagine it being as much of a draw to attraction like cobra at chessington. Im not a fan of the carnival theme its something that drayton manor could get away with though, towers I for 1 expect either a strong and original theme now days, or a good IP themed area, Whatever they do though. I just hope they do try like as a whole merlin has done pretty good latley, so I do trust whatever they do with CCL in the future. Still think it will be about 5 years till they start any work there though.