The plans and that artist impression (3rd photo down) shows the entrance from the departure lounge going through what is now the middle of the duty free shop. The original idea when the terminal was built was that passengers would pass along the full length of the glass fronted rear passageway that sits behind the shops.
Most of the new shops will be located from the top of the stairs, through what is now the security area and into the new build before reaching the present departure lounge. Also instead of walking is a straight line the route will be snake shaped to maximize the number of retail outlets.
I think Stansted has has just opened a similar arrangement where all departing passengers have to walk through a shopping centre first.
The airport seems to be going more up market no doubt to improve its passenger ratings.