Agree
The current standard is that a minimum radius of 360m is advised for platforms, with a radius of 200m the absolute limit. The documentation I have doesn't show the radius for St John's directly (possibly because it's never a constant radius), but does show the curves at Bedford Midland to St John's as 250m minimum radius, and Bletchley to Fenny Stratford as 550m minimum radius. If BSJ is only being served by 3/4 car local trains, the derivation to the lower value of the standards is possible.
Here's a photo showing the area is slightly more detail. You're absolutely right that 2 tracks + platforms under the bridge is not going to happen, but 2 tracks on their own can, and possibly at W10/12 clearance. Note the gradient of the road, and proximity of the T junction on the left making rebuilding the bridge very expensive/disruptive. The track is very, very likely to need to be doubled to permit the proposed service. If that happens, the platform under the bridge has to go. So then the choice is either to close the station completely or to resite it. The houses are less than 100m from the existing station, and surrounded by industrial units. I suspect if they are given the choice between closure or the station being nearer, they'd opt for the latter. From the look of St John's car park (out of shot) even if the local houses did object, there'd still be more than enough support from the wider area to justify proceeding, with suitable mitigation in place for those next to the line. You're correct the residents' views cannot be just ignored, but neither can they prevent the station being rebuilt.
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