a footbridge still wouldn't solve the accessability problem for people with mobility problems, buggies etc - unless it had lifts each side which would be really expensive (and unreliable). I think the answer lies with the subway, which I understand is going to be improved by the people developing the new flats. I am not sure what they are gong to do with it - it would be difficult (impossible?) to make it step free. I believe there will be lifts to get over the tracks in FH station when it gets done up, but you will need an Oyster card to use them!!
I think the car park certainly allows ample room for a ramp to be used for a footbridge. The other side is indeed a little more restricted, but im sure a spiral ramp like in ladywell park could be effective.
The plans for the subway sound rather empty, and I agree, the longer flight near WH Smiths is a little harder to resolve, would be one hell of a steep ramp.
As for the station and lifts, that should be fun to see. Station could do with an overhaul. As for the Oyster card users only, but of course !