That concept was part of the previous Middlesbrough Council led masterplan. The real world site constraints meant that a new platform and concourse to the north of the up/down slow lines was never a feasible option.That appears different from what I was expecting. I was under the impression a new platform was getting built on the north side (down Saltburn slow line).
I've attached some detailed initial drawings, which outline the proposed arrangement for the new platform and track layout. These are still awaiting sign off by Network Rail's engineering and asset management teams, so could be subject to change, but they're a good barometer for what to expect from the package of works: