The GNSS procedure is still being worked through. When introducing a new procedure there are multiple layers to go through (some would call them hoops!) The CAP725 consultation is just the start of proceedings, you then need to get the procedure designed, validate the procedure, carry out further obstacle surveys and then work to mitigate against any issues that the regulator may come up with. Once all of this is complete you can then enter the procedure into the AIRAC cycle which takes another 2 months before the first aeroplane can fly it.
It's fair to say that following the consultation, the airport did not expect the rest to take as long as it has. It's still a work in progress and they are working through a number of items to complete the final safety case. You also need to make sure that your partner airlines have the technology to be able to fly the procedure!
One important point to note is that the minima will not improve greatly. The implementation of the GNSS approach is to provide a resilient and future proofed procedure following the national removal of the DVOR's by NATS.