Dkc, I think that the vertical posts supporting the roof of the John Street Stand go up fairly close to the fronts of the 'executive' boxes, so that they would get in the way if they were replaced by seats.
The thing is, when they built the South Stand on the old cricket pitch, they deliberately left a big gap between the front of it and the pitch. This was so they could nudge the pitch towards the south stand and build another stand the same size on the John Street side, a good idea you'd agree.
BUT they didn't use all the space they had when they did rebuild the JJS. I think this was because it would have blocked the views of some of the seats on the kop and the Bramall Lane stands. In any of the new developments at the ground, they have never demolished parts of adjacent stands to allow for a neater fit. This is why the corner between John Street and the Kop is such a bad fit, it could have been perfect but you would have had to either lose a bit of the kop or the JSS.
Had the JSS been closer to the South Stand, as was originally planned, it could have been built higher. The closer the stand is to the houses, the lower it must be to cast the same length of shadow on those houses.
It just goes to show that the planning of the stadium is as disjointed as that of the team over the past 40 years and I don't know the contractual ins and outs but I believe the John Street stand was completed to fulfill a contract long after it had been realised that it was NOT the best solution for the site. It was a 'design and build contract' meaning that the contractors built to their own design rather than SUFC commissioning a design and then going out to tender to find a builder.
In other words, to some extent, the club lost control over what was built . It was always, "sub-optimal".