I don't know the answer to the question and would be interested to hear opinions. I've copied below the drawings published by the project team last year as an 'example'
It is not completely clear what goes where but the proposal seems to be staircase plus lift.
That these plans have been drawn up in the first place could suggest that fully reopening the tunnel isn't practical and may have been ruled out as might not be possible to make it fully accessible.
What isn't clear from these drawings is have they taken into account the new housing by the line and its access rights, will station buildings and the cafe need to be demolished, can electricity sub-stations be moved and what compulsory purchases will be necessary — the builder's yard clearly will have to be taken over.