The original stadium masterplan had covered stands behind both ends. And interestingly enough that plan still gets referred to in lots of the planning application detail which in theory means the council have bought into it - but the reality of getting something approved is most likely rather different.
The published version of the masterplan was an artist's impression rather than a detailed layout so it's hard to see how they squeezed that west stand in- my suspicion has always been that, since it only provided for a single tier east stand, the proposed west end was only feasible by shifting the pitch eastwards a little.
Clearly the Carnegie Stand ended up being altogether more substantial and built on the existing touchline which may mean there now just isn't scope for anything of note at the western end without house demolition. (I do wonder if Caddick hasn't spent 20 years buying up some property round there though.)
One thing which the masterplan appears to suggest, although it's not totally clear, was opening up the ginnell to a small open plan plaza fronted by turnstiles to the stand. Given how irredeemably unlovely the ginnell presently is, suggesting something similar could get the club a bit of favour with planning. How that might then tie in with the back side of what has actually been built on the cricket side I don't know.
Lastly the masterplan provided for a proper, full size North Stand. The planning application for what is actually being built there is almost apologetic for deviating from this aspect, as well it might be. The west end is always going to be tricky but I do think we'll look back on what has been done on the north side as an unfortunate missed opportunity a few years down the line and one which will be monstrously expensive to fix.