On March 11, 2020, LGWM ('Let's Get Wellingron Moving') announced that Aurecon and Future Group would design and plan an extra Mt Victoria tunnel (and some other roads) supported by by local experts, from GHD and Jacobs.

Press release of LGWM reads:

The contract for the state highway work has been awarded to a team with extensive experience in New Zealand infrastructure projects from Aurecon and Future Group (a consortium of Stantec, Jasmax, WSP and Boffa Miskell). The contract for the mass rapid transit work has been awarded to a strong international team, supported by local experts, from GHD and Jacobs.
This initial business case work is expected to be completed in early 2021.
The estimated combined investment in mass rapid transit and state highway improvements will be NZD $3 billion.

Wellington mayor had earlier called for the extra Mt Victoria tunnel project to be brought forward. It is estimated that the construction of the extra Mt Victoria tunnel itself will cost around NZD 700 million including the upgrade of some roads feeding it. In 2019, the Transport Minister Phil Twyford had said that the extra Mt Victoria tunnel would be prioritised for buses, cyclists, and pedestrians.

https://lgwm.nz/lgwm-news/work-underway-on-mass-rapid-transit-and-state-highway-projects/

(map from google maps)