I think it's come to realisation that the forced-flow retail layout isn't really conducive to additional spending. WDF is a different story as that's the norm almost everywhere and I wouldn't expect that to fundamentally change. In most airports once leaving WDF, you're into an open retail/dining space, but STN (and LTN) take it a step further with much of the general retail continuing with the same forced-flow concept. To an extent it was designed like that because it allows more floor space for retail use in a fairly constrained area. Plus it means there are no "hot" or "cold" spots since every passenger passes through/by every retail unit, which also helps contractual agreements with the retailers.
Going forwards, and I have no detail/confirmation of this, but I have heard the existing retail layout maybe reconfigured at some point as well. The aforementioned space constraints are adressed by the terminal extension and the corridor through much of the existing retail area will likely be too narrow for the number of passengers in future going through it (I would argue it already is). The future thinking from what I've heard is a move to a more open space and a line-of-sight to the retail offering, much like what you see in the artist impressions.