I agree about platform 3 middle road. But there must be an explanation as to why it wasn't kept.
I'm not quite sure, if that is an old foundation where it would have come from. It's about half way down the platform and really the only structure which might have needed a foundation of that size would be the old signal gantries at the east end?
I was thinking about this yesterday also whether having two bays instead of the old platform 4 actually does that much for capacity. Part of the reason for the work at the west end - Mansfield Jn is obviously to ensure that trains to/from Radford Jn can use the north side (P1/3) and trains from Beeston the south side, without the need for crossed paths. If this is the case then consider the length and nature of trains using the station:
North side - Radford Junction
RHL - 2tph terminating (2 coaches average)
Leeds - 1tph terminating (2 coaches)
Liverpool - Norwich - 1tph mostly through (4 coaches west 2 east)
South side - Beeston
London Fast - 1tph terminating (2+8 HST)
London semi-fast - 1tph terminating (5 coaches)*
Birmingham XC - 2tph terminating (3 coaches)*
Matlock - 1tph terminating (2 coaches)
Lincoln - Leicester 1tph mostly through
Through freight as required
*Some require ECS shunts at Nottingham for capacity purposes
Here's what the new layout will look like. Terminating trains from the north could use platforms 4 and 5, but I can see them probably using 1 or 3, because of the number of trains coming from the south. I wonder if it would be handy were the Norwich trains to use the same platform. This would mean that units splitting/joining wouldn't have to move platforms as was the case with the old layout. Leeds and Mansfield trains might not be able to share the same platform with their current times but the platform for Norwich services may also have some spare capacity.
My issue really is with platforms 4-7. I can't remember the lengths of the new platforms 4 and 5 off the top of my head but I'm assuming platform 5 will fit 5 cars. So, the current 222 could park up in 5, the HST 6. I don't think that the paths of the two XC trains allow them to use the same platform, one could be platform 7, the Cardiff train platform 6. Question then is what will use platform 4 - I think it would be a shame were the Matlock trains having to use platform 4 when approaching from the west. Undoubtedly the Lincoln trains (and Skegness if not platform 2) could use 4 and the Leicester trains 7 potentially if it doesn't clash with others.
Of course you also have that issue of freight which has to come through Nottingham, for example the Rectory oil trains. Part of me wonders whether platform 3 middle road will be missed, not just for stabling trains but for through freights. But I can't also help wonder - with the number of longer trains terminating it would seem on the south side of the station whether platform 3 would have been a more appropriate candidate as a bay instead of platform 4? It seems to me that having one long platform provides more flexibility than two bays. Either that or keep (old) platform 4 but install a scissor crossover off the middle road.
Anyway, what's done is (nearly) done. It's either that or trains from the south use the northern platforms or vice versa, as I said my understanding that that wasn't intended in order to increase capacity. But time will tell...