Holds in CTA would be an excellent idea, but obviously all the SIDS and STARS will need to be changed.(that needs to be done holds or not). One to the north and one south would be an excellent start, however that would mean Minhad closing and Dubai getting that portion of CTA. Not ever going to happen, right??
Stacks work at EGLL and EGKK, because the controller basically runs a procedural approach. He descends aircraft to the next level when it has been reported vacated, the strip bay is displayed by a camera link to the TMA controllers so they can see what level is available for the next inbounds etc. Means your strip marking has to be spot on. Plus the approach controller and "stack" controller share the same frequency, so they know what is happening, takes good team work.
The thing I am noticing from this thread that there are loads of good ideas to improve the ATC system. Basically we all know that the current one is not acceptable and if things keep growing at this amazing rate and things don't change then we are going to have a lot of planes sitting on the tarmac going nowhere, and loads of aircraft diverting due to fuel shortages!!!!