The construction of a taxiway is very much different from that of a runway. It's much cheaper to build and maintain a taxiway than a runway. Rwy 23 has been designated part of twy alpha for a little while now according to the aerodrome chart in the air pilot. Officially 23 is still available but if it costs 1 dep and 1 arr slot to let something land on 23, who would let that happen these days?
Also there's bound to be legal wrangles when they start planning for the 3rd (4th in theory) runway. I suspect 23 will remain on the book until it is built so they can say "hey we havent added another runway, we've simply relocated 23 to become the new 27R"!!!