Good idea.
The problem is the over-hanging WHSmiths extension - I think that would get in the way. Otherwise there would be plenty of room for a long ramp starting from underneath the track.

Alternatively, if the South circ was narrowed at the junction - and there is a good case for that anyway - there would be additional pavement width to help accommodate a ramp.

Or they could have embedded a lift in the stair side wall, as was suggested when the council had bucket-fulls of cash from the PV central development.

Or there is the 'anyone with a buggy/disabled/old/and all pedestrians and cyclists can just FO' option, which seems to have been the preferred choice of late. And people do indeed go elsewhere, and our shops suffer for it.