Changing OLE gantries is very unlikely, I agree with
@The Planner (Although Google Satellite/Street View images suggest the 4ft of the loop is clear, but they may be outdated).
The widest part of the platform island measures c.8m on google maps. Current standards require 2m unobstructed width from the platform edge on lines up to 100mph and 2.5m above 100mph, IIRC. As the Chase line is 30mph and the Down Trent Valley Slow is 110mph, this gives c.3.5m for a lift shaft.
According to this (10-year-old) document:
https://assets.publishing.service.g...be5d/design-standards-accessible-stations.pdf, a lift with internal dimensions of 2m width and 1.4m depth allows a wheelchair to be rotated. So there seems to be just about room if the lift shaft is reasonably thin. It would require quite a lot of platform furniture to be relocated, but there does seem to be width for a lift and the landing (just).
I do, however, agree with
@SCDR_WMR in post #6 that the available width is unlikely to be sufficient for steps and a lift shaft to the same bridge, so the existing non-accessible bridge would probably need to be retained. I also can see huge issues with constructability (likely requiring closure of the Chase line platform while the lift is built, and probably some changes to the Trent Valley platform), and Signal Sighting - the bridge will need to be tall enough to clear the down signals and even then the curve may mean that an additional banner repeater is required for the Down Slow. Both of these have the potential to make it a very very difficult case for investment.
Slueing the chase line over and widening the platform would be ideal but as others have said it's not going to happen. Another option if a completely new bridge were to be required including steps would be to shorten the operational length of the Chase Line platform with railings. But that would likely need to be done at the north end as the south end looks too narrow even for a single-sided platform. However, it's currently only about 100m long so any further shortening would probably not be viable for the possible lengths of Chase Line services.

[Image of Rugeley Trent Valley Station with 8m width highlighted in Red and potential landing area on Up Side highlighted in purple]