If the runway extension ever happens, and that is a BIG if, the area required is already within the aerodrome boundary. It won't affect the race circuit.
Owners MAG do not spend money without a rock-solid business case. They already have a long £200 million runway about 70 miles to the North-West which is seriously under-utilised. The original project for the 3100 metre EMA runway date back to National Express ownership. MAG sensibly deferred the last 150 metres when they took ownership in 2000. Keeping the planning permission warm probably helps the asset value of EMA and hence the recent renewal.