In what way is the video not encouraging? There was always going to be significant rail work required to transport containers from Wangarei down to Auckland. Unless I missed something in the video, the planning and physical work to improve the rail line is continuing and gaining speed.
Some of the bridges may need to close in 5 years without safety work being done - but doesn't the video say two bridges are being replaced so the problem is being solved?
Of course current freight volumes don't justify the spending, they will primarily be from what Northland imports from Auckland and what Northland ships down to Auckland. If the port is shifted, this equation flips and becomes what Auckland imports from Northland and what Auckland ships up to Northland. Auckland is of course a lot larger than Northland so the second equation is a lot bigger, hence more traffic on the railway line in forward looking scenarios.
I'm speculating here, but I suspect cabinet rather than just ministerial sign-off would have been required for this package of work. The accompanying commentary to get this sign-off is likely to have noted that its only a sensible infrastructure investment if freight is moved from Ports of Auckland. The proposal was agreed.