Holborn station is 100 years old, although it was significantly altered in 1933 when the original lifts were replaced with escalators.
Looking at the 3D diagram of the station [1] it seems the original lift shafts didn't go to platform level anyway, and are now used as emergency stairs and a ventilation shaft.
Even if it's possible to add lifts, and even if the expense isn't astronomical, it would still only make sense if it could be done for many stations on the line — but most of them are this old, and handling far more passengers than ever anticipated.
Looking at the 3D diagram of the station [1] it seems the original lift shafts didn't go to platform level anyway, and are now used as emergency stairs and a ventilation shaft.
Even if it's possible to add lifts, and even if the expense isn't astronomical, it would still only make sense if it could be done for many stations on the line — but most of them are this old, and handling far more passengers than ever anticipated.
[1] http://www.ianvisits.co.uk/blog/2015/07/12/3d-maps-of-every-...