What’s ultimately needed on the Northside is a 5th & 6th track to Airport junction and a 4th track to Petrie. (Either by expanding the existing corridor or equivalent in bypass corridor.)
That allows for shifting sector boundaries to rebalance CBD capacity: Airport + Doomben with Ferny Grove on sector 3, Redcliffe (perhaps split at Petrie) goes with Shorncliffe on sector 2, Caboolture + Sunshine Coast via CRR on sector 1.
If there’s a bypass corridor (e.g. a Chermside tunnel) freight and long distance QR presumably won’t be using it just like they won’t be using CRR, so they will be a cross-sector move. But presumably they won’t be running through in the middle of peak hour, either. Plus, if there is a bypass corridor, the 3rd track north of Northgate becomes available for freight/LD.
Long term we should also be looking to see a 3rd track through the Petrie-Caboolture section, doing basically the same things the Petrie-Northgate 3rd track does today.
Any potential bypass corridor would be a tunnelling effort of similar magnitude as CRR. But it won’t cross the river so I don’t think of it as CRR 2.